diff --git a/.github/workflows/basic.yml b/.github/workflows/basic.yml
index 773cb928..cb9cb4ee 100644
--- a/.github/workflows/basic.yml
+++ b/.github/workflows/basic.yml
@@ -41,7 +41,7 @@ jobs:
           conda config --add channels conda-forge
           conda config --set channel_priority strict
           conda info
-          conda install python==3.9 pytorch==1.13.0 pytest numpy -y
+          conda install python==3.9 pytorch==1.13.0 pytest numpy hypothesis -y
           conda list
           conda config --show-sources
       #    conda config --show
diff --git a/torch_np/__init__.py b/torch_np/__init__.py
index a4900d44..f9c9a8eb 100644
--- a/torch_np/__init__.py
+++ b/torch_np/__init__.py
@@ -14,6 +14,8 @@
 nan = float("nan")
 
 
+alltrue = all
+
 #### HACK HACK HACK ####
 import torch
 
diff --git a/torch_np/testing/__init__.py b/torch_np/testing/__init__.py
index 26c94ca9..7ca601c2 100644
--- a/torch_np/testing/__init__.py
+++ b/torch_np/testing/__init__.py
@@ -3,9 +3,12 @@
     assert_,
     assert_allclose,
     assert_almost_equal,
+    assert_array_almost_equal,
     assert_array_equal,
     assert_equal,
+    assert_raises_regex,
     assert_warns,
+    suppress_warnings,
 )
 
 # from .testing import assert_allclose    # FIXME
diff --git a/torch_np/tests/numpy_tests/lib/test_function_base.py b/torch_np/tests/numpy_tests/lib/test_function_base.py
new file mode 100644
index 00000000..f9a3d608
--- /dev/null
+++ b/torch_np/tests/numpy_tests/lib/test_function_base.py
@@ -0,0 +1,3985 @@
+import operator
+import warnings
+import sys
+import decimal
+from fractions import Fraction
+import math
+import pytest
+import hypothesis
+from hypothesis.extra.numpy import arrays
+import hypothesis.strategies as st
+
+
+import torch_np as np
+# from numpy import ma
+from torch_np.testing import (assert_, assert_equal, assert_array_equal, assert_almost_equal,
+    assert_array_almost_equal, assert_allclose, # IS_PYPY,
+    assert_warns, assert_raises_regex, suppress_warnings, # HAS_REFCOUNT, IS_WASM
+    )
+from pytest import raises as assert_raises
+
+HAS_REFCOUNT = True
+IS_WASM = False
+IS_PYPY = False
+
+import numpy.lib.function_base as nfb   # FIXME: remove
+from numpy.random import rand    # FIXME: random.rand
+
+
+# FIXME: make from torch_np
+from numpy.lib import (
+    add_newdoc_ufunc, angle, average, bartlett, blackman, corrcoef, cov,
+    delete, diff, digitize, extract, flipud, gradient, hamming, hanning,
+    i0, insert, interp, kaiser, meshgrid, msort, piecewise, place, rot90,
+    select, setxor1d, sinc, trapz, trim_zeros, unwrap, unique, vectorize
+    )
+from torch_np._util import normalize_axis_tuple
+
+
+def get_mat(n):
+    data = np.arange(n)
+    data = np.add.outer(data, data)
+    return data
+
+
+def _make_complex(real, imag):
+    """
+    Like real + 1j * imag, but behaves as expected when imag contains non-finite
+    values
+    """
+    ret = np.zeros(np.broadcast(real, imag).shape, np.complex_)
+    ret.real = real
+    ret.imag = imag
+    return ret
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestRot90:
+    def test_basic(self):
+        assert_raises(ValueError, rot90, np.ones(4))
+        assert_raises(ValueError, rot90, np.ones((2,2,2)), axes=(0,1,2))
+        assert_raises(ValueError, rot90, np.ones((2,2)), axes=(0,2))
+        assert_raises(ValueError, rot90, np.ones((2,2)), axes=(1,1))
+        assert_raises(ValueError, rot90, np.ones((2,2,2)), axes=(-2,1))
+
+        a = [[0, 1, 2],
+             [3, 4, 5]]
+        b1 = [[2, 5],
+              [1, 4],
+              [0, 3]]
+        b2 = [[5, 4, 3],
+              [2, 1, 0]]
+        b3 = [[3, 0],
+              [4, 1],
+              [5, 2]]
+        b4 = [[0, 1, 2],
+              [3, 4, 5]]
+
+        for k in range(-3, 13, 4):
+            assert_equal(rot90(a, k=k), b1)
+        for k in range(-2, 13, 4):
+            assert_equal(rot90(a, k=k), b2)
+        for k in range(-1, 13, 4):
+            assert_equal(rot90(a, k=k), b3)
+        for k in range(0, 13, 4):
+            assert_equal(rot90(a, k=k), b4)
+
+        assert_equal(rot90(rot90(a, axes=(0,1)), axes=(1,0)), a)
+        assert_equal(rot90(a, k=1, axes=(1,0)), rot90(a, k=-1, axes=(0,1)))
+
+    def test_axes(self):
+        a = np.ones((50, 40, 3))
+        assert_equal(rot90(a).shape, (40, 50, 3))
+        assert_equal(rot90(a, axes=(0,2)), rot90(a, axes=(0,-1)))
+        assert_equal(rot90(a, axes=(1,2)), rot90(a, axes=(-2,-1)))
+
+    def test_rotation_axes(self):
+        a = np.arange(8).reshape((2,2,2))
+
+        a_rot90_01 = [[[2, 3],
+                       [6, 7]],
+                      [[0, 1],
+                       [4, 5]]]
+        a_rot90_12 = [[[1, 3],
+                       [0, 2]],
+                      [[5, 7],
+                       [4, 6]]]
+        a_rot90_20 = [[[4, 0],
+                       [6, 2]],
+                      [[5, 1],
+                       [7, 3]]]
+        a_rot90_10 = [[[4, 5],
+                       [0, 1]],
+                      [[6, 7],
+                       [2, 3]]]
+
+        assert_equal(rot90(a, axes=(0, 1)), a_rot90_01)
+        assert_equal(rot90(a, axes=(1, 0)), a_rot90_10)
+        assert_equal(rot90(a, axes=(1, 2)), a_rot90_12)
+
+        for k in range(1,5):
+            assert_equal(rot90(a, k=k, axes=(2, 0)),
+                         rot90(a_rot90_20, k=k-1, axes=(2, 0)))
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestFlip:
+
+    def test_axes(self):
+        assert_raises(np.AxisError, np.flip, np.ones(4), axis=1)
+        assert_raises(np.AxisError, np.flip, np.ones((4, 4)), axis=2)
+        assert_raises(np.AxisError, np.flip, np.ones((4, 4)), axis=-3)
+        assert_raises(np.AxisError, np.flip, np.ones((4, 4)), axis=(0, 3))
+
+    def test_basic_lr(self):
+        a = get_mat(4)
+        b = a[:, ::-1]
+        assert_equal(np.flip(a, 1), b)
+        a = [[0, 1, 2],
+             [3, 4, 5]]
+        b = [[2, 1, 0],
+             [5, 4, 3]]
+        assert_equal(np.flip(a, 1), b)
+
+    def test_basic_ud(self):
+        a = get_mat(4)
+        b = a[::-1, :]
+        assert_equal(np.flip(a, 0), b)
+        a = [[0, 1, 2],
+             [3, 4, 5]]
+        b = [[3, 4, 5],
+             [0, 1, 2]]
+        assert_equal(np.flip(a, 0), b)
+
+    def test_3d_swap_axis0(self):
+        a = np.array([[[0, 1],
+                       [2, 3]],
+                      [[4, 5],
+                       [6, 7]]])
+
+        b = np.array([[[4, 5],
+                       [6, 7]],
+                      [[0, 1],
+                       [2, 3]]])
+
+        assert_equal(np.flip(a, 0), b)
+
+    def test_3d_swap_axis1(self):
+        a = np.array([[[0, 1],
+                       [2, 3]],
+                      [[4, 5],
+                       [6, 7]]])
+
+        b = np.array([[[2, 3],
+                       [0, 1]],
+                      [[6, 7],
+                       [4, 5]]])
+
+        assert_equal(np.flip(a, 1), b)
+
+    def test_3d_swap_axis2(self):
+        a = np.array([[[0, 1],
+                       [2, 3]],
+                      [[4, 5],
+                       [6, 7]]])
+
+        b = np.array([[[1, 0],
+                       [3, 2]],
+                      [[5, 4],
+                       [7, 6]]])
+
+        assert_equal(np.flip(a, 2), b)
+
+    def test_4d(self):
+        a = np.arange(2 * 3 * 4 * 5).reshape(2, 3, 4, 5)
+        for i in range(a.ndim):
+            assert_equal(np.flip(a, i),
+                         np.flipud(a.swapaxes(0, i)).swapaxes(i, 0))
+
+    def test_default_axis(self):
+        a = np.array([[1, 2, 3],
+                      [4, 5, 6]])
+        b = np.array([[6, 5, 4],
+                      [3, 2, 1]])
+        assert_equal(np.flip(a), b)
+
+    def test_multiple_axes(self):
+        a = np.array([[[0, 1],
+                       [2, 3]],
+                      [[4, 5],
+                       [6, 7]]])
+
+        assert_equal(np.flip(a, axis=()), a)
+
+        b = np.array([[[5, 4],
+                       [7, 6]],
+                      [[1, 0],
+                       [3, 2]]])
+
+        assert_equal(np.flip(a, axis=(0, 2)), b)
+
+        c = np.array([[[3, 2],
+                       [1, 0]],
+                      [[7, 6],
+                       [5, 4]]])
+
+        assert_equal(np.flip(a, axis=(1, 2)), c)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestAny:
+
+    def test_basic(self):
+        y1 = [0, 0, 1, 0]
+        y2 = [0, 0, 0, 0]
+        y3 = [1, 0, 1, 0]
+        assert_(np.any(y1))
+        assert_(np.any(y3))
+        assert_(not np.any(y2))
+
+    def test_nd(self):
+        y1 = [[0, 0, 0], [0, 1, 0], [1, 1, 0]]
+        assert_(np.any(y1))
+        assert_array_equal(np.sometrue(y1, axis=0), [1, 1, 0])
+        assert_array_equal(np.sometrue(y1, axis=1), [0, 1, 1])
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestAll:
+
+    def test_basic(self):
+        y1 = [0, 1, 1, 0]
+        y2 = [0, 0, 0, 0]
+        y3 = [1, 1, 1, 1]
+        assert_(not np.all(y1))
+        assert_(np.all(y3))
+        assert_(not np.all(y2))
+        assert_(np.all(~np.array(y2)))
+
+    def test_nd(self):
+        y1 = [[0, 0, 1], [0, 1, 1], [1, 1, 1]]
+        assert_(not np.all(y1))
+        assert_array_equal(np.alltrue(y1, axis=0), [0, 0, 1])
+        assert_array_equal(np.alltrue(y1, axis=1), [0, 0, 1])
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestCopy:
+
+    def test_basic(self):
+        a = np.array([[1, 2], [3, 4]])
+        a_copy = np.copy(a)
+        assert_array_equal(a, a_copy)
+        a_copy[0, 0] = 10
+        assert_equal(a[0, 0], 1)
+        assert_equal(a_copy[0, 0], 10)
+
+    def test_order(self):
+        # It turns out that people rely on np.copy() preserving order by
+        # default; changing this broke scikit-learn:
+        # github.com/scikit-learn/scikit-learn/commit/7842748cf777412c506a8c0ed28090711d3a3783  # noqa
+        a = np.array([[1, 2], [3, 4]])
+        assert_(a.flags.c_contiguous)
+        assert_(not a.flags.f_contiguous)
+        a_fort = np.array([[1, 2], [3, 4]], order="F")
+        assert_(not a_fort.flags.c_contiguous)
+        assert_(a_fort.flags.f_contiguous)
+        a_copy = np.copy(a)
+        assert_(a_copy.flags.c_contiguous)
+        assert_(not a_copy.flags.f_contiguous)
+        a_fort_copy = np.copy(a_fort)
+        assert_(not a_fort_copy.flags.c_contiguous)
+        assert_(a_fort_copy.flags.f_contiguous)
+
+    def test_subok(self):
+        mx = ma.ones(5)
+        assert_(not ma.isMaskedArray(np.copy(mx, subok=False)))
+        assert_(ma.isMaskedArray(np.copy(mx, subok=True)))
+        # Default behavior
+        assert_(not ma.isMaskedArray(np.copy(mx)))
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestAverage:
+
+    def test_basic(self):
+        y1 = np.array([1, 2, 3])
+        assert_(average(y1, axis=0) == 2.)
+        y2 = np.array([1., 2., 3.])
+        assert_(average(y2, axis=0) == 2.)
+        y3 = [0., 0., 0.]
+        assert_(average(y3, axis=0) == 0.)
+
+        y4 = np.ones((4, 4))
+        y4[0, 1] = 0
+        y4[1, 0] = 2
+        assert_almost_equal(y4.mean(0), average(y4, 0))
+        assert_almost_equal(y4.mean(1), average(y4, 1))
+
+        y5 = rand(5, 5)
+        assert_almost_equal(y5.mean(0), average(y5, 0))
+        assert_almost_equal(y5.mean(1), average(y5, 1))
+
+    @pytest.mark.parametrize(
+        'x, axis, expected_avg, weights, expected_wavg, expected_wsum',
+        [([1, 2, 3], None, [2.0], [3, 4, 1], [1.75], [8.0]),
+         ([[1, 2, 5], [1, 6, 11]], 0, [[1.0, 4.0, 8.0]],
+          [1, 3], [[1.0, 5.0, 9.5]], [[4, 4, 4]])],
+    )
+    def test_basic_keepdims(self, x, axis, expected_avg,
+                            weights, expected_wavg, expected_wsum):
+        avg = np.average(x, axis=axis, keepdims=True)
+        assert avg.shape == np.shape(expected_avg)
+        assert_array_equal(avg, expected_avg)
+
+        wavg = np.average(x, axis=axis, weights=weights, keepdims=True)
+        assert wavg.shape == np.shape(expected_wavg)
+        assert_array_equal(wavg, expected_wavg)
+
+        wavg, wsum = np.average(x, axis=axis, weights=weights, returned=True,
+                                keepdims=True)
+        assert wavg.shape == np.shape(expected_wavg)
+        assert_array_equal(wavg, expected_wavg)
+        assert wsum.shape == np.shape(expected_wsum)
+        assert_array_equal(wsum, expected_wsum)
+
+    def test_weights(self):
+        y = np.arange(10)
+        w = np.arange(10)
+        actual = average(y, weights=w)
+        desired = (np.arange(10) ** 2).sum() * 1. / np.arange(10).sum()
+        assert_almost_equal(actual, desired)
+
+        y1 = np.array([[1, 2, 3], [4, 5, 6]])
+        w0 = [1, 2]
+        actual = average(y1, weights=w0, axis=0)
+        desired = np.array([3., 4., 5.])
+        assert_almost_equal(actual, desired)
+
+        w1 = [0, 0, 1]
+        actual = average(y1, weights=w1, axis=1)
+        desired = np.array([3., 6.])
+        assert_almost_equal(actual, desired)
+
+        # This should raise an error. Can we test for that ?
+        # assert_equal(average(y1, weights=w1), 9./2.)
+
+        # 2D Case
+        w2 = [[0, 0, 1], [0, 0, 2]]
+        desired = np.array([3., 6.])
+        assert_array_equal(average(y1, weights=w2, axis=1), desired)
+        assert_equal(average(y1, weights=w2), 5.)
+
+        y3 = rand(5).astype(np.float32)
+        w3 = rand(5).astype(np.float64)
+
+        assert_(np.average(y3, weights=w3).dtype == np.result_type(y3, w3))
+
+        # test weights with `keepdims=False` and `keepdims=True`
+        x = np.array([2, 3, 4]).reshape(3, 1)
+        w = np.array([4, 5, 6]).reshape(3, 1)
+
+        actual = np.average(x, weights=w, axis=1, keepdims=False)
+        desired = np.array([2., 3., 4.])
+        assert_array_equal(actual, desired)
+
+        actual = np.average(x, weights=w, axis=1, keepdims=True)
+        desired = np.array([[2.], [3.], [4.]])
+        assert_array_equal(actual, desired)
+
+    def test_returned(self):
+        y = np.array([[1, 2, 3], [4, 5, 6]])
+
+        # No weights
+        avg, scl = average(y, returned=True)
+        assert_equal(scl, 6.)
+
+        avg, scl = average(y, 0, returned=True)
+        assert_array_equal(scl, np.array([2., 2., 2.]))
+
+        avg, scl = average(y, 1, returned=True)
+        assert_array_equal(scl, np.array([3., 3.]))
+
+        # With weights
+        w0 = [1, 2]
+        avg, scl = average(y, weights=w0, axis=0, returned=True)
+        assert_array_equal(scl, np.array([3., 3., 3.]))
+
+        w1 = [1, 2, 3]
+        avg, scl = average(y, weights=w1, axis=1, returned=True)
+        assert_array_equal(scl, np.array([6., 6.]))
+
+        w2 = [[0, 0, 1], [1, 2, 3]]
+        avg, scl = average(y, weights=w2, axis=1, returned=True)
+        assert_array_equal(scl, np.array([1., 6.]))
+
+    def test_subclasses(self):
+        class subclass(np.ndarray):
+            pass
+        a = np.array([[1,2],[3,4]]).view(subclass)
+        w = np.array([[1,2],[3,4]]).view(subclass)
+
+        assert_equal(type(np.average(a)), subclass)
+        assert_equal(type(np.average(a, weights=w)), subclass)
+
+    def test_upcasting(self):
+        typs = [('i4', 'i4', 'f8'), ('i4', 'f4', 'f8'), ('f4', 'i4', 'f8'),
+                 ('f4', 'f4', 'f4'), ('f4', 'f8', 'f8')]
+        for at, wt, rt in typs:
+            a = np.array([[1,2],[3,4]], dtype=at)
+            w = np.array([[1,2],[3,4]], dtype=wt)
+            assert_equal(np.average(a, weights=w).dtype, np.dtype(rt))
+
+    def test_object_dtype(self):
+        a = np.array([decimal.Decimal(x) for x in range(10)])
+        w = np.array([decimal.Decimal(1) for _ in range(10)])
+        w /= w.sum()
+        assert_almost_equal(a.mean(0), average(a, weights=w))
+
+    def test_average_class_without_dtype(self):
+        # see gh-21988
+        a = np.array([Fraction(1, 5), Fraction(3, 5)])
+        assert_equal(np.average(a), Fraction(2, 5))
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestSelect:
+    choices = [np.array([1, 2, 3]),
+               np.array([4, 5, 6]),
+               np.array([7, 8, 9])]
+    conditions = [np.array([False, False, False]),
+                  np.array([False, True, False]),
+                  np.array([False, False, True])]
+
+    def _select(self, cond, values, default=0):
+        output = []
+        for m in range(len(cond)):
+            output += [V[m] for V, C in zip(values, cond) if C[m]] or [default]
+        return output
+
+    def test_basic(self):
+        choices = self.choices
+        conditions = self.conditions
+        assert_array_equal(select(conditions, choices, default=15),
+                           self._select(conditions, choices, default=15))
+
+        assert_equal(len(choices), 3)
+        assert_equal(len(conditions), 3)
+
+    def test_broadcasting(self):
+        conditions = [np.array(True), np.array([False, True, False])]
+        choices = [1, np.arange(12).reshape(4, 3)]
+        assert_array_equal(select(conditions, choices), np.ones((4, 3)))
+        # default can broadcast too:
+        assert_equal(select([True], [0], default=[0]).shape, (1,))
+
+    def test_return_dtype(self):
+        assert_equal(select(self.conditions, self.choices, 1j).dtype,
+                     np.complex_)
+        # But the conditions need to be stronger then the scalar default
+        # if it is scalar.
+        choices = [choice.astype(np.int8) for choice in self.choices]
+        assert_equal(select(self.conditions, choices).dtype, np.int8)
+
+        d = np.array([1, 2, 3, np.nan, 5, 7])
+        m = np.isnan(d)
+        assert_equal(select([m], [d]), [0, 0, 0, np.nan, 0, 0])
+
+    def test_deprecated_empty(self):
+        assert_raises(ValueError, select, [], [], 3j)
+        assert_raises(ValueError, select, [], [])
+
+    def test_non_bool_deprecation(self):
+        choices = self.choices
+        conditions = self.conditions[:]
+        conditions[0] = conditions[0].astype(np.int_)
+        assert_raises(TypeError, select, conditions, choices)
+        conditions[0] = conditions[0].astype(np.uint8)
+        assert_raises(TypeError, select, conditions, choices)
+        assert_raises(TypeError, select, conditions, choices)
+
+    def test_many_arguments(self):
+        # This used to be limited by NPY_MAXARGS == 32
+        conditions = [np.array([False])] * 100
+        choices = [np.array([1])] * 100
+        select(conditions, choices)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestInsert:
+
+    def test_basic(self):
+        a = [1, 2, 3]
+        assert_equal(insert(a, 0, 1), [1, 1, 2, 3])
+        assert_equal(insert(a, 3, 1), [1, 2, 3, 1])
+        assert_equal(insert(a, [1, 1, 1], [1, 2, 3]), [1, 1, 2, 3, 2, 3])
+        assert_equal(insert(a, 1, [1, 2, 3]), [1, 1, 2, 3, 2, 3])
+        assert_equal(insert(a, [1, -1, 3], 9), [1, 9, 2, 9, 3, 9])
+        assert_equal(insert(a, slice(-1, None, -1), 9), [9, 1, 9, 2, 9, 3])
+        assert_equal(insert(a, [-1, 1, 3], [7, 8, 9]), [1, 8, 2, 7, 3, 9])
+        b = np.array([0, 1], dtype=np.float64)
+        assert_equal(insert(b, 0, b[0]), [0., 0., 1.])
+        assert_equal(insert(b, [], []), b)
+        # Bools will be treated differently in the future:
+        # assert_equal(insert(a, np.array([True]*4), 9), [9, 1, 9, 2, 9, 3, 9])
+        with warnings.catch_warnings(record=True) as w:
+            warnings.filterwarnings('always', '', FutureWarning)
+            assert_equal(
+                insert(a, np.array([True] * 4), 9), [1, 9, 9, 9, 9, 2, 3])
+            assert_(w[0].category is FutureWarning)
+
+    def test_multidim(self):
+        a = [[1, 1, 1]]
+        r = [[2, 2, 2],
+             [1, 1, 1]]
+        assert_equal(insert(a, 0, [1]), [1, 1, 1, 1])
+        assert_equal(insert(a, 0, [2, 2, 2], axis=0), r)
+        assert_equal(insert(a, 0, 2, axis=0), r)
+        assert_equal(insert(a, 2, 2, axis=1), [[1, 1, 2, 1]])
+
+        a = np.array([[1, 1], [2, 2], [3, 3]])
+        b = np.arange(1, 4).repeat(3).reshape(3, 3)
+        c = np.concatenate(
+            (a[:, 0:1], np.arange(1, 4).repeat(3).reshape(3, 3).T,
+             a[:, 1:2]), axis=1)
+        assert_equal(insert(a, [1], [[1], [2], [3]], axis=1), b)
+        assert_equal(insert(a, [1], [1, 2, 3], axis=1), c)
+        # scalars behave differently, in this case exactly opposite:
+        assert_equal(insert(a, 1, [1, 2, 3], axis=1), b)
+        assert_equal(insert(a, 1, [[1], [2], [3]], axis=1), c)
+
+        a = np.arange(4).reshape(2, 2)
+        assert_equal(insert(a[:, :1], 1, a[:, 1], axis=1), a)
+        assert_equal(insert(a[:1,:], 1, a[1,:], axis=0), a)
+
+        # negative axis value
+        a = np.arange(24).reshape((2, 3, 4))
+        assert_equal(insert(a, 1, a[:,:, 3], axis=-1),
+                     insert(a, 1, a[:,:, 3], axis=2))
+        assert_equal(insert(a, 1, a[:, 2,:], axis=-2),
+                     insert(a, 1, a[:, 2,:], axis=1))
+
+        # invalid axis value
+        assert_raises(np.AxisError, insert, a, 1, a[:, 2, :], axis=3)
+        assert_raises(np.AxisError, insert, a, 1, a[:, 2, :], axis=-4)
+
+        # negative axis value
+        a = np.arange(24).reshape((2, 3, 4))
+        assert_equal(insert(a, 1, a[:, :, 3], axis=-1),
+                     insert(a, 1, a[:, :, 3], axis=2))
+        assert_equal(insert(a, 1, a[:, 2, :], axis=-2),
+                     insert(a, 1, a[:, 2, :], axis=1))
+
+    def test_0d(self):
+        a = np.array(1)
+        with pytest.raises(np.AxisError):
+            insert(a, [], 2, axis=0)
+        with pytest.raises(TypeError):
+            insert(a, [], 2, axis="nonsense")
+
+    def test_subclass(self):
+        class SubClass(np.ndarray):
+            pass
+        a = np.arange(10).view(SubClass)
+        assert_(isinstance(np.insert(a, 0, [0]), SubClass))
+        assert_(isinstance(np.insert(a, [], []), SubClass))
+        assert_(isinstance(np.insert(a, [0, 1], [1, 2]), SubClass))
+        assert_(isinstance(np.insert(a, slice(1, 2), [1, 2]), SubClass))
+        assert_(isinstance(np.insert(a, slice(1, -2, -1), []), SubClass))
+        # This is an error in the future:
+        a = np.array(1).view(SubClass)
+        assert_(isinstance(np.insert(a, 0, [0]), SubClass))
+
+    def test_index_array_copied(self):
+        x = np.array([1, 1, 1])
+        np.insert([0, 1, 2], x, [3, 4, 5])
+        assert_equal(x, np.array([1, 1, 1]))
+
+    def test_structured_array(self):
+        a = np.array([(1, 'a'), (2, 'b'), (3, 'c')],
+                     dtype=[('foo', 'i'), ('bar', 'a1')])
+        val = (4, 'd')
+        b = np.insert(a, 0, val)
+        assert_array_equal(b[0], np.array(val, dtype=b.dtype))
+        val = [(4, 'd')] * 2
+        b = np.insert(a, [0, 2], val)
+        assert_array_equal(b[[0, 3]], np.array(val, dtype=b.dtype))
+
+    def test_index_floats(self):
+        with pytest.raises(IndexError):
+            np.insert([0, 1, 2], np.array([1.0, 2.0]), [10, 20])
+        with pytest.raises(IndexError):
+            np.insert([0, 1, 2], np.array([], dtype=float), [])
+
+    @pytest.mark.parametrize('idx', [4, -4])
+    def test_index_out_of_bounds(self, idx):
+        with pytest.raises(IndexError, match='out of bounds'):
+            np.insert([0, 1, 2], [idx], [3, 4])
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestAmax:
+
+    def test_basic(self):
+        a = [3, 4, 5, 10, -3, -5, 6.0]
+        assert_equal(np.amax(a), 10.0)
+        b = [[3, 6.0, 9.0],
+             [4, 10.0, 5.0],
+             [8, 3.0, 2.0]]
+        assert_equal(np.amax(b, axis=0), [8.0, 10.0, 9.0])
+        assert_equal(np.amax(b, axis=1), [9.0, 10.0, 8.0])
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestAmin:
+
+    def test_basic(self):
+        a = [3, 4, 5, 10, -3, -5, 6.0]
+        assert_equal(np.amin(a), -5.0)
+        b = [[3, 6.0, 9.0],
+             [4, 10.0, 5.0],
+             [8, 3.0, 2.0]]
+        assert_equal(np.amin(b, axis=0), [3.0, 3.0, 2.0])
+        assert_equal(np.amin(b, axis=1), [3.0, 4.0, 2.0])
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestPtp:
+
+    def test_basic(self):
+        a = np.array([3, 4, 5, 10, -3, -5, 6.0])
+        assert_equal(a.ptp(axis=0), 15.0)
+        b = np.array([[3, 6.0, 9.0],
+                      [4, 10.0, 5.0],
+                      [8, 3.0, 2.0]])
+        assert_equal(b.ptp(axis=0), [5.0, 7.0, 7.0])
+        assert_equal(b.ptp(axis=-1), [6.0, 6.0, 6.0])
+
+        assert_equal(b.ptp(axis=0, keepdims=True), [[5.0, 7.0, 7.0]])
+        assert_equal(b.ptp(axis=(0,1), keepdims=True), [[8.0]])
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestCumsum:
+
+    def test_basic(self):
+        ba = [1, 2, 10, 11, 6, 5, 4]
+        ba2 = [[1, 2, 3, 4], [5, 6, 7, 9], [10, 3, 4, 5]]
+        for ctype in [np.int8, np.uint8, np.int16, np.int32,
+                      np.float32, np.float64, np.complex64,
+                      np.complex128]:
+            a = np.array(ba, ctype)
+            a2 = np.array(ba2, ctype)
+
+            tgt = np.array([1, 3, 13, 24, 30, 35, 39], ctype)
+            assert_array_equal(np.cumsum(a, axis=0), tgt)
+
+            tgt = np.array(
+                [[1, 2, 3, 4], [6, 8, 10, 13], [16, 11, 14, 18]], ctype)
+            assert_array_equal(np.cumsum(a2, axis=0), tgt)
+
+            tgt = np.array(
+                [[1, 3, 6, 10], [5, 11, 18, 27], [10, 13, 17, 22]], ctype)
+            assert_array_equal(np.cumsum(a2, axis=1), tgt)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestProd:
+
+    def test_basic(self):
+        ba = [1, 2, 10, 11, 6, 5, 4]
+        ba2 = [[1, 2, 3, 4], [5, 6, 7, 9], [10, 3, 4, 5]]
+        for ctype in [np.int16, np.int32,
+                      np.float32, np.float64, np.complex64, np.complex128]:
+            a = np.array(ba, ctype)
+            a2 = np.array(ba2, ctype)
+            if ctype in ['1', 'b']:
+                assert_raises(ArithmeticError, np.prod, a)
+                assert_raises(ArithmeticError, np.prod, a2, 1)
+            else:
+                assert_equal(a.prod(axis=0), 26400)
+                assert_array_equal(a2.prod(axis=0),
+                                   np.array([50, 36, 84, 180], ctype))
+                assert_array_equal(a2.prod(axis=-1),
+                                   np.array([24, 1890, 600], ctype))
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestCumprod:
+
+    def test_basic(self):
+        ba = [1, 2, 10, 11, 6, 5, 4]
+        ba2 = [[1, 2, 3, 4], [5, 6, 7, 9], [10, 3, 4, 5]]
+        for ctype in [np.int16, np.int32,
+                      np.float32, np.float64, np.complex64, np.complex128]:
+            a = np.array(ba, ctype)
+            a2 = np.array(ba2, ctype)
+            if ctype in ['1', 'b']:
+                assert_raises(ArithmeticError, np.cumprod, a)
+                assert_raises(ArithmeticError, np.cumprod, a2, 1)
+                assert_raises(ArithmeticError, np.cumprod, a)
+            else:
+                assert_array_equal(np.cumprod(a, axis=-1),
+                                   np.array([1, 2, 20, 220,
+                                             1320, 6600, 26400], ctype))
+                assert_array_equal(np.cumprod(a2, axis=0),
+                                   np.array([[1, 2, 3, 4],
+                                             [5, 12, 21, 36],
+                                             [50, 36, 84, 180]], ctype))
+                assert_array_equal(np.cumprod(a2, axis=-1),
+                                   np.array([[1, 2, 6, 24],
+                                             [5, 30, 210, 1890],
+                                             [10, 30, 120, 600]], ctype))
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestDiff:
+
+    def test_basic(self):
+        x = [1, 4, 6, 7, 12]
+        out = np.array([3, 2, 1, 5])
+        out2 = np.array([-1, -1, 4])
+        out3 = np.array([0, 5])
+        assert_array_equal(diff(x), out)
+        assert_array_equal(diff(x, n=2), out2)
+        assert_array_equal(diff(x, n=3), out3)
+
+        x = [1.1, 2.2, 3.0, -0.2, -0.1]
+        out = np.array([1.1, 0.8, -3.2, 0.1])
+        assert_almost_equal(diff(x), out)
+
+        x = [True, True, False, False]
+        out = np.array([False, True, False])
+        out2 = np.array([True, True])
+        assert_array_equal(diff(x), out)
+        assert_array_equal(diff(x, n=2), out2)
+
+    def test_axis(self):
+        x = np.zeros((10, 20, 30))
+        x[:, 1::2, :] = 1
+        exp = np.ones((10, 19, 30))
+        exp[:, 1::2, :] = -1
+        assert_array_equal(diff(x), np.zeros((10, 20, 29)))
+        assert_array_equal(diff(x, axis=-1), np.zeros((10, 20, 29)))
+        assert_array_equal(diff(x, axis=0), np.zeros((9, 20, 30)))
+        assert_array_equal(diff(x, axis=1), exp)
+        assert_array_equal(diff(x, axis=-2), exp)
+        assert_raises(np.AxisError, diff, x, axis=3)
+        assert_raises(np.AxisError, diff, x, axis=-4)
+
+        x = np.array(1.11111111111, np.float64)
+        assert_raises(ValueError, diff, x)
+
+    def test_nd(self):
+        x = 20 * rand(10, 20, 30)
+        out1 = x[:, :, 1:] - x[:, :, :-1]
+        out2 = out1[:, :, 1:] - out1[:, :, :-1]
+        out3 = x[1:, :, :] - x[:-1, :, :]
+        out4 = out3[1:, :, :] - out3[:-1, :, :]
+        assert_array_equal(diff(x), out1)
+        assert_array_equal(diff(x, n=2), out2)
+        assert_array_equal(diff(x, axis=0), out3)
+        assert_array_equal(diff(x, n=2, axis=0), out4)
+
+    def test_n(self):
+        x = list(range(3))
+        assert_raises(ValueError, diff, x, n=-1)
+        output = [diff(x, n=n) for n in range(1, 5)]
+        expected = [[1, 1], [0], [], []]
+        assert_(diff(x, n=0) is x)
+        for n, (expected, out) in enumerate(zip(expected, output), start=1):
+            assert_(type(out) is np.ndarray)
+            assert_array_equal(out, expected)
+            assert_equal(out.dtype, np.int_)
+            assert_equal(len(out), max(0, len(x) - n))
+
+    def test_times(self):
+        x = np.arange('1066-10-13', '1066-10-16', dtype=np.datetime64)
+        expected = [
+            np.array([1, 1], dtype='timedelta64[D]'),
+            np.array([0], dtype='timedelta64[D]'),
+        ]
+        expected.extend([np.array([], dtype='timedelta64[D]')] * 3)
+        for n, exp in enumerate(expected, start=1):
+            out = diff(x, n=n)
+            assert_array_equal(out, exp)
+            assert_equal(out.dtype, exp.dtype)
+
+    def test_subclass(self):
+        x = ma.array([[1, 2], [3, 4], [5, 6], [7, 8], [9, 10]],
+                     mask=[[False, False], [True, False],
+                           [False, True], [True, True], [False, False]])
+        out = diff(x)
+        assert_array_equal(out.data, [[1], [1], [1], [1], [1]])
+        assert_array_equal(out.mask, [[False], [True],
+                                      [True], [True], [False]])
+        assert_(type(out) is type(x))
+
+        out3 = diff(x, n=3)
+        assert_array_equal(out3.data, [[], [], [], [], []])
+        assert_array_equal(out3.mask, [[], [], [], [], []])
+        assert_(type(out3) is type(x))
+
+    def test_prepend(self):
+        x = np.arange(5) + 1
+        assert_array_equal(diff(x, prepend=0), np.ones(5))
+        assert_array_equal(diff(x, prepend=[0]), np.ones(5))
+        assert_array_equal(np.cumsum(np.diff(x, prepend=0)), x)
+        assert_array_equal(diff(x, prepend=[-1, 0]), np.ones(6))
+
+        x = np.arange(4).reshape(2, 2)
+        result = np.diff(x, axis=1, prepend=0)
+        expected = [[0, 1], [2, 1]]
+        assert_array_equal(result, expected)
+        result = np.diff(x, axis=1, prepend=[[0], [0]])
+        assert_array_equal(result, expected)
+
+        result = np.diff(x, axis=0, prepend=0)
+        expected = [[0, 1], [2, 2]]
+        assert_array_equal(result, expected)
+        result = np.diff(x, axis=0, prepend=[[0, 0]])
+        assert_array_equal(result, expected)
+
+        assert_raises(ValueError, np.diff, x, prepend=np.zeros((3,3)))
+
+        assert_raises(np.AxisError, diff, x, prepend=0, axis=3)
+
+    def test_append(self):
+        x = np.arange(5)
+        result = diff(x, append=0)
+        expected = [1, 1, 1, 1, -4]
+        assert_array_equal(result, expected)
+        result = diff(x, append=[0])
+        assert_array_equal(result, expected)
+        result = diff(x, append=[0, 2])
+        expected = expected + [2]
+        assert_array_equal(result, expected)
+
+        x = np.arange(4).reshape(2, 2)
+        result = np.diff(x, axis=1, append=0)
+        expected = [[1, -1], [1, -3]]
+        assert_array_equal(result, expected)
+        result = np.diff(x, axis=1, append=[[0], [0]])
+        assert_array_equal(result, expected)
+
+        result = np.diff(x, axis=0, append=0)
+        expected = [[2, 2], [-2, -3]]
+        assert_array_equal(result, expected)
+        result = np.diff(x, axis=0, append=[[0, 0]])
+        assert_array_equal(result, expected)
+
+        assert_raises(ValueError, np.diff, x, append=np.zeros((3,3)))
+
+        assert_raises(np.AxisError, diff, x, append=0, axis=3)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestDelete:
+
+    def setup_method(self):
+        self.a = np.arange(5)
+        self.nd_a = np.arange(5).repeat(2).reshape(1, 5, 2)
+
+    def _check_inverse_of_slicing(self, indices):
+        a_del = delete(self.a, indices)
+        nd_a_del = delete(self.nd_a, indices, axis=1)
+        msg = 'Delete failed for obj: %r' % indices
+        assert_array_equal(setxor1d(a_del, self.a[indices, ]), self.a,
+                           err_msg=msg)
+        xor = setxor1d(nd_a_del[0,:, 0], self.nd_a[0, indices, 0])
+        assert_array_equal(xor, self.nd_a[0,:, 0], err_msg=msg)
+
+    def test_slices(self):
+        lims = [-6, -2, 0, 1, 2, 4, 5]
+        steps = [-3, -1, 1, 3]
+        for start in lims:
+            for stop in lims:
+                for step in steps:
+                    s = slice(start, stop, step)
+                    self._check_inverse_of_slicing(s)
+
+    def test_fancy(self):
+        self._check_inverse_of_slicing(np.array([[0, 1], [2, 1]]))
+        with pytest.raises(IndexError):
+            delete(self.a, [100])
+        with pytest.raises(IndexError):
+            delete(self.a, [-100])
+
+        self._check_inverse_of_slicing([0, -1, 2, 2])
+
+        self._check_inverse_of_slicing([True, False, False, True, False])
+
+        # not legal, indexing with these would change the dimension
+        with pytest.raises(ValueError):
+            delete(self.a, True)
+        with pytest.raises(ValueError):
+            delete(self.a, False)
+
+        # not enough items
+        with pytest.raises(ValueError):
+            delete(self.a, [False]*4)
+
+    def test_single(self):
+        self._check_inverse_of_slicing(0)
+        self._check_inverse_of_slicing(-4)
+
+    def test_0d(self):
+        a = np.array(1)
+        with pytest.raises(np.AxisError):
+            delete(a, [], axis=0)
+        with pytest.raises(TypeError):
+            delete(a, [], axis="nonsense")
+
+    def test_subclass(self):
+        class SubClass(np.ndarray):
+            pass
+        a = self.a.view(SubClass)
+        assert_(isinstance(delete(a, 0), SubClass))
+        assert_(isinstance(delete(a, []), SubClass))
+        assert_(isinstance(delete(a, [0, 1]), SubClass))
+        assert_(isinstance(delete(a, slice(1, 2)), SubClass))
+        assert_(isinstance(delete(a, slice(1, -2)), SubClass))
+
+    def test_array_order_preserve(self):
+        # See gh-7113
+        k = np.arange(10).reshape(2, 5, order='F')
+        m = delete(k, slice(60, None), axis=1)
+
+        # 'k' is Fortran ordered, and 'm' should have the
+        # same ordering as 'k' and NOT become C ordered
+        assert_equal(m.flags.c_contiguous, k.flags.c_contiguous)
+        assert_equal(m.flags.f_contiguous, k.flags.f_contiguous)
+
+    def test_index_floats(self):
+        with pytest.raises(IndexError):
+            np.delete([0, 1, 2], np.array([1.0, 2.0]))
+        with pytest.raises(IndexError):
+            np.delete([0, 1, 2], np.array([], dtype=float))
+
+    @pytest.mark.parametrize("indexer", [np.array([1]), [1]])
+    def test_single_item_array(self, indexer):
+        a_del_int = delete(self.a, 1)
+        a_del = delete(self.a, indexer)
+        assert_equal(a_del_int, a_del)
+
+        nd_a_del_int = delete(self.nd_a, 1, axis=1)
+        nd_a_del = delete(self.nd_a, np.array([1]), axis=1)
+        assert_equal(nd_a_del_int, nd_a_del)
+
+    def test_single_item_array_non_int(self):
+        # Special handling for integer arrays must not affect non-integer ones.
+        # If `False` was cast to `0` it would delete the element:
+        res = delete(np.ones(1), np.array([False]))
+        assert_array_equal(res, np.ones(1))
+
+        # Test the more complicated (with axis) case from gh-21840
+        x = np.ones((3, 1))
+        false_mask = np.array([False], dtype=bool)
+        true_mask = np.array([True], dtype=bool)
+
+        res = delete(x, false_mask, axis=-1)
+        assert_array_equal(res, x)
+        res = delete(x, true_mask, axis=-1)
+        assert_array_equal(res, x[:, :0])
+
+        # Object or e.g. timedeltas should *not* be allowed
+        with pytest.raises(IndexError):
+            delete(np.ones(2), np.array([0], dtype=object))
+
+        with pytest.raises(IndexError):
+            # timedeltas are sometimes "integral, but clearly not allowed:
+            delete(np.ones(2), np.array([0], dtype="m8[ns]"))
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestGradient:
+
+    def test_basic(self):
+        v = [[1, 1], [3, 4]]
+        x = np.array(v)
+        dx = [np.array([[2., 3.], [2., 3.]]),
+              np.array([[0., 0.], [1., 1.]])]
+        assert_array_equal(gradient(x), dx)
+        assert_array_equal(gradient(v), dx)
+
+    def test_args(self):
+        dx = np.cumsum(np.ones(5))
+        dx_uneven = [1., 2., 5., 9., 11.]
+        f_2d = np.arange(25).reshape(5, 5)
+
+        # distances must be scalars or have size equal to gradient[axis]
+        gradient(np.arange(5), 3.)
+        gradient(np.arange(5), np.array(3.))
+        gradient(np.arange(5), dx)
+        # dy is set equal to dx because scalar
+        gradient(f_2d, 1.5)
+        gradient(f_2d, np.array(1.5))
+
+        gradient(f_2d, dx_uneven, dx_uneven)
+        # mix between even and uneven spaces and
+        # mix between scalar and vector
+        gradient(f_2d, dx, 2)
+
+        # 2D but axis specified
+        gradient(f_2d, dx, axis=1)
+
+        # 2d coordinate arguments are not yet allowed
+        assert_raises_regex(ValueError, '.*scalars or 1d',
+            gradient, f_2d, np.stack([dx]*2, axis=-1), 1)
+
+    def test_badargs(self):
+        f_2d = np.arange(25).reshape(5, 5)
+        x = np.cumsum(np.ones(5))
+
+        # wrong sizes
+        assert_raises(ValueError, gradient, f_2d, x, np.ones(2))
+        assert_raises(ValueError, gradient, f_2d, 1, np.ones(2))
+        assert_raises(ValueError, gradient, f_2d, np.ones(2), np.ones(2))
+        # wrong number of arguments
+        assert_raises(TypeError, gradient, f_2d, x)
+        assert_raises(TypeError, gradient, f_2d, x, axis=(0,1))
+        assert_raises(TypeError, gradient, f_2d, x, x, x)
+        assert_raises(TypeError, gradient, f_2d, 1, 1, 1)
+        assert_raises(TypeError, gradient, f_2d, x, x, axis=1)
+        assert_raises(TypeError, gradient, f_2d, 1, 1, axis=1)
+
+    def test_datetime64(self):
+        # Make sure gradient() can handle special types like datetime64
+        x = np.array(
+            ['1910-08-16', '1910-08-11', '1910-08-10', '1910-08-12',
+             '1910-10-12', '1910-12-12', '1912-12-12'],
+            dtype='datetime64[D]')
+        dx = np.array(
+            [-5, -3, 0, 31, 61, 396, 731],
+            dtype='timedelta64[D]')
+        assert_array_equal(gradient(x), dx)
+        assert_(dx.dtype == np.dtype('timedelta64[D]'))
+
+    def test_masked(self):
+        # Make sure that gradient supports subclasses like masked arrays
+        x = np.ma.array([[1, 1], [3, 4]],
+                        mask=[[False, False], [False, False]])
+        out = gradient(x)[0]
+        assert_equal(type(out), type(x))
+        # And make sure that the output and input don't have aliased mask
+        # arrays
+        assert_(x._mask is not out._mask)
+        # Also check that edge_order=2 doesn't alter the original mask
+        x2 = np.ma.arange(5)
+        x2[2] = np.ma.masked
+        np.gradient(x2, edge_order=2)
+        assert_array_equal(x2.mask, [False, False, True, False, False])
+
+    def test_second_order_accurate(self):
+        # Testing that the relative numerical error is less that 3% for
+        # this example problem. This corresponds to second order
+        # accurate finite differences for all interior and boundary
+        # points.
+        x = np.linspace(0, 1, 10)
+        dx = x[1] - x[0]
+        y = 2 * x ** 3 + 4 * x ** 2 + 2 * x
+        analytical = 6 * x ** 2 + 8 * x + 2
+        num_error = np.abs((np.gradient(y, dx, edge_order=2) / analytical) - 1)
+        assert_(np.all(num_error < 0.03) == True)
+
+        # test with unevenly spaced
+        np.random.seed(0)
+        x = np.sort(np.random.random(10))
+        y = 2 * x ** 3 + 4 * x ** 2 + 2 * x
+        analytical = 6 * x ** 2 + 8 * x + 2
+        num_error = np.abs((np.gradient(y, x, edge_order=2) / analytical) - 1)
+        assert_(np.all(num_error < 0.03) == True)
+
+    def test_spacing(self):
+        f = np.array([0, 2., 3., 4., 5., 5.])
+        f = np.tile(f, (6,1)) + f.reshape(-1, 1)
+        x_uneven = np.array([0., 0.5, 1., 3., 5., 7.])
+        x_even = np.arange(6.)
+
+        fdx_even_ord1 = np.tile([2., 1.5, 1., 1., 0.5, 0.], (6,1))
+        fdx_even_ord2 = np.tile([2.5, 1.5, 1., 1., 0.5, -0.5], (6,1))
+        fdx_uneven_ord1 = np.tile([4., 3., 1.7, 0.5, 0.25, 0.], (6,1))
+        fdx_uneven_ord2 = np.tile([5., 3., 1.7, 0.5, 0.25, -0.25], (6,1))
+
+        # evenly spaced
+        for edge_order, exp_res in [(1, fdx_even_ord1), (2, fdx_even_ord2)]:
+            res1 = gradient(f, 1., axis=(0,1), edge_order=edge_order)
+            res2 = gradient(f, x_even, x_even,
+                            axis=(0,1), edge_order=edge_order)
+            res3 = gradient(f, x_even, x_even,
+                            axis=None, edge_order=edge_order)
+            assert_array_equal(res1, res2)
+            assert_array_equal(res2, res3)
+            assert_almost_equal(res1[0], exp_res.T)
+            assert_almost_equal(res1[1], exp_res)
+
+            res1 = gradient(f, 1., axis=0, edge_order=edge_order)
+            res2 = gradient(f, x_even, axis=0, edge_order=edge_order)
+            assert_(res1.shape == res2.shape)
+            assert_almost_equal(res2, exp_res.T)
+
+            res1 = gradient(f, 1., axis=1, edge_order=edge_order)
+            res2 = gradient(f, x_even, axis=1, edge_order=edge_order)
+            assert_(res1.shape == res2.shape)
+            assert_array_equal(res2, exp_res)
+
+        # unevenly spaced
+        for edge_order, exp_res in [(1, fdx_uneven_ord1), (2, fdx_uneven_ord2)]:
+            res1 = gradient(f, x_uneven, x_uneven,
+                            axis=(0,1), edge_order=edge_order)
+            res2 = gradient(f, x_uneven, x_uneven,
+                            axis=None, edge_order=edge_order)
+            assert_array_equal(res1, res2)
+            assert_almost_equal(res1[0], exp_res.T)
+            assert_almost_equal(res1[1], exp_res)
+
+            res1 = gradient(f, x_uneven, axis=0, edge_order=edge_order)
+            assert_almost_equal(res1, exp_res.T)
+
+            res1 = gradient(f, x_uneven, axis=1, edge_order=edge_order)
+            assert_almost_equal(res1, exp_res)
+
+        # mixed
+        res1 = gradient(f, x_even, x_uneven, axis=(0,1), edge_order=1)
+        res2 = gradient(f, x_uneven, x_even, axis=(1,0), edge_order=1)
+        assert_array_equal(res1[0], res2[1])
+        assert_array_equal(res1[1], res2[0])
+        assert_almost_equal(res1[0], fdx_even_ord1.T)
+        assert_almost_equal(res1[1], fdx_uneven_ord1)
+
+        res1 = gradient(f, x_even, x_uneven, axis=(0,1), edge_order=2)
+        res2 = gradient(f, x_uneven, x_even, axis=(1,0), edge_order=2)
+        assert_array_equal(res1[0], res2[1])
+        assert_array_equal(res1[1], res2[0])
+        assert_almost_equal(res1[0], fdx_even_ord2.T)
+        assert_almost_equal(res1[1], fdx_uneven_ord2)
+
+    def test_specific_axes(self):
+        # Testing that gradient can work on a given axis only
+        v = [[1, 1], [3, 4]]
+        x = np.array(v)
+        dx = [np.array([[2., 3.], [2., 3.]]),
+              np.array([[0., 0.], [1., 1.]])]
+        assert_array_equal(gradient(x, axis=0), dx[0])
+        assert_array_equal(gradient(x, axis=1), dx[1])
+        assert_array_equal(gradient(x, axis=-1), dx[1])
+        assert_array_equal(gradient(x, axis=(1, 0)), [dx[1], dx[0]])
+
+        # test axis=None which means all axes
+        assert_almost_equal(gradient(x, axis=None), [dx[0], dx[1]])
+        # and is the same as no axis keyword given
+        assert_almost_equal(gradient(x, axis=None), gradient(x))
+
+        # test vararg order
+        assert_array_equal(gradient(x, 2, 3, axis=(1, 0)),
+                           [dx[1]/2.0, dx[0]/3.0])
+        # test maximal number of varargs
+        assert_raises(TypeError, gradient, x, 1, 2, axis=1)
+
+        assert_raises(np.AxisError, gradient, x, axis=3)
+        assert_raises(np.AxisError, gradient, x, axis=-3)
+        # assert_raises(TypeError, gradient, x, axis=[1,])
+
+    def test_timedelta64(self):
+        # Make sure gradient() can handle special types like timedelta64
+        x = np.array(
+            [-5, -3, 10, 12, 61, 321, 300],
+            dtype='timedelta64[D]')
+        dx = np.array(
+            [2, 7, 7, 25, 154, 119, -21],
+            dtype='timedelta64[D]')
+        assert_array_equal(gradient(x), dx)
+        assert_(dx.dtype == np.dtype('timedelta64[D]'))
+
+    def test_inexact_dtypes(self):
+        for dt in [np.float16, np.float32, np.float64]:
+            # dtypes should not be promoted in a different way to what diff does
+            x = np.array([1, 2, 3], dtype=dt)
+            assert_equal(gradient(x).dtype, np.diff(x).dtype)
+
+    def test_values(self):
+        # needs at least 2 points for edge_order ==1
+        gradient(np.arange(2), edge_order=1)
+        # needs at least 3 points for edge_order ==1
+        gradient(np.arange(3), edge_order=2)
+
+        assert_raises(ValueError, gradient, np.arange(0), edge_order=1)
+        assert_raises(ValueError, gradient, np.arange(0), edge_order=2)
+        assert_raises(ValueError, gradient, np.arange(1), edge_order=1)
+        assert_raises(ValueError, gradient, np.arange(1), edge_order=2)
+        assert_raises(ValueError, gradient, np.arange(2), edge_order=2)
+
+    @pytest.mark.parametrize('f_dtype', [np.uint8, ])
+    def test_f_decreasing_unsigned_int(self, f_dtype):
+        f = np.array([5, 4, 3, 2, 1], dtype=f_dtype)
+        g = gradient(f)
+        assert_array_equal(g, [-1]*len(f))
+
+    @pytest.mark.parametrize('f_dtype', [np.int8, np.int16,
+                                         np.int32, np.int64])
+    def test_f_signed_int_big_jump(self, f_dtype):
+        maxint = np.iinfo(f_dtype).max
+        x = np.array([1, 3])
+        f = np.array([-1, maxint], dtype=f_dtype)
+        dfdx = gradient(f, x)
+        assert_array_equal(dfdx, [(maxint + 1) // 2]*2)
+
+    @pytest.mark.parametrize('x_dtype', [np.uint8, ])
+    def test_x_decreasing_unsigned(self, x_dtype):
+        x = np.array([3, 2, 1], dtype=x_dtype)
+        f = np.array([0, 2, 4])
+        dfdx = gradient(f, x)
+        assert_array_equal(dfdx, [-2]*len(x))
+
+    @pytest.mark.parametrize('x_dtype', [np.int8, np.int16,
+                                         np.int32, np.int64])
+    def test_x_signed_int_big_jump(self, x_dtype):
+        minint = np.iinfo(x_dtype).min
+        maxint = np.iinfo(x_dtype).max
+        x = np.array([-1, maxint], dtype=x_dtype)
+        f = np.array([minint // 2, 0])
+        dfdx = gradient(f, x)
+        assert_array_equal(dfdx, [0.5, 0.5])
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestAngle:
+
+    def test_basic(self):
+        x = [1 + 3j, np.sqrt(2) / 2.0 + 1j * np.sqrt(2) / 2,
+             1, 1j, -1, -1j, 1 - 3j, -1 + 3j]
+        y = angle(x)
+        yo = [
+            np.arctan(3.0 / 1.0),
+            np.arctan(1.0), 0, np.pi / 2, np.pi, -np.pi / 2.0,
+            -np.arctan(3.0 / 1.0), np.pi - np.arctan(3.0 / 1.0)]
+        z = angle(x, deg=True)
+        zo = np.array(yo) * 180 / np.pi
+        assert_array_almost_equal(y, yo, 11)
+        assert_array_almost_equal(z, zo, 11)
+
+    def test_subclass(self):
+        x = np.ma.array([1 + 3j, 1, np.sqrt(2)/2 * (1 + 1j)])
+        x[1] = np.ma.masked
+        expected = np.ma.array([np.arctan(3.0 / 1.0), 0, np.arctan(1.0)])
+        expected[1] = np.ma.masked
+        actual = angle(x)
+        assert_equal(type(actual), type(expected))
+        assert_equal(actual.mask, expected.mask)
+        assert_equal(actual, expected)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestTrimZeros:
+
+    a = np.array([0, 0, 1, 0, 2, 3, 4, 0])
+    b = a.astype(float)
+    c = a.astype(complex)
+#    d = a.astype(object)
+
+    def values(self):
+        attr_names = ('a', 'b', 'c', 'd')
+        return (getattr(self, name) for name in attr_names)
+
+    def test_basic(self):
+        slc = np.s_[2:-1]
+        for arr in self.values():
+            res = trim_zeros(arr)
+            assert_array_equal(res, arr[slc])
+
+    def test_leading_skip(self):
+        slc = np.s_[:-1]
+        for arr in self.values():
+            res = trim_zeros(arr, trim='b')
+            assert_array_equal(res, arr[slc])
+
+    def test_trailing_skip(self):
+        slc = np.s_[2:]
+        for arr in self.values():
+            res = trim_zeros(arr, trim='F')
+            assert_array_equal(res, arr[slc])
+
+    def test_all_zero(self):
+        for _arr in self.values():
+            arr = np.zeros_like(_arr, dtype=_arr.dtype)
+
+            res1 = trim_zeros(arr, trim='B')
+            assert len(res1) == 0
+
+            res2 = trim_zeros(arr, trim='f')
+            assert len(res2) == 0
+
+    def test_size_zero(self):
+        arr = np.zeros(0)
+        res = trim_zeros(arr)
+        assert_array_equal(arr, res)
+
+    @pytest.mark.parametrize(
+        'arr',
+        [np.array([0, 2**62, 0]),
+#         np.array([0, 2**63, 0]),     # FIXME
+#         np.array([0, 2**64, 0])
+        ])
+    def test_overflow(self, arr):
+        slc = np.s_[1:2]
+        res = trim_zeros(arr)
+        assert_array_equal(res, arr[slc])
+
+    def test_no_trim(self):
+        arr = np.array([None, 1, None])
+        res = trim_zeros(arr)
+        assert_array_equal(arr, res)
+
+    def test_list_to_list(self):
+        res = trim_zeros(self.a.tolist())
+        assert isinstance(res, list)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestExtins:
+
+    def test_basic(self):
+        a = np.array([1, 3, 2, 1, 2, 3, 3])
+        b = extract(a > 1, a)
+        assert_array_equal(b, [3, 2, 2, 3, 3])
+
+    def test_place(self):
+        # Make sure that non-np.ndarray objects
+        # raise an error instead of doing nothing
+        assert_raises(TypeError, place, [1, 2, 3], [True, False], [0, 1])
+
+        a = np.array([1, 4, 3, 2, 5, 8, 7])
+        place(a, [0, 1, 0, 1, 0, 1, 0], [2, 4, 6])
+        assert_array_equal(a, [1, 2, 3, 4, 5, 6, 7])
+
+        place(a, np.zeros(7), [])
+        assert_array_equal(a, np.arange(1, 8))
+
+        place(a, [1, 0, 1, 0, 1, 0, 1], [8, 9])
+        assert_array_equal(a, [8, 2, 9, 4, 8, 6, 9])
+        assert_raises_regex(ValueError, "Cannot insert from an empty array",
+                            lambda: place(a, [0, 0, 0, 0, 0, 1, 0], []))
+
+        # See Issue #6974
+        a = np.array(['12', '34'])
+        place(a, [0, 1], '9')
+        assert_array_equal(a, ['12', '9'])
+
+    def test_both(self):
+        a = rand(10)
+        mask = a > 0.5
+        ac = a.copy()
+        c = extract(mask, a)
+        place(a, mask, 0)
+        place(a, mask, c)
+        assert_array_equal(a, ac)
+
+
+# _foo1 and _foo2 are used in some tests in TestVectorize.
+
+def _foo1(x, y=1.0):
+    return y*math.floor(x)
+
+
+def _foo2(x, y=1.0, z=0.0):
+    return y*math.floor(x) + z
+
+
+@pytest.mark.skip(reason='vectorize not implemented')
+class TestVectorize:
+
+    def test_simple(self):
+        def addsubtract(a, b):
+            if a > b:
+                return a - b
+            else:
+                return a + b
+
+        f = vectorize(addsubtract)
+        r = f([0, 3, 6, 9], [1, 3, 5, 7])
+        assert_array_equal(r, [1, 6, 1, 2])
+
+    def test_scalar(self):
+        def addsubtract(a, b):
+            if a > b:
+                return a - b
+            else:
+                return a + b
+
+        f = vectorize(addsubtract)
+        r = f([0, 3, 6, 9], 5)
+        assert_array_equal(r, [5, 8, 1, 4])
+
+    def test_large(self):
+        x = np.linspace(-3, 2, 10000)
+        f = vectorize(lambda x: x)
+        y = f(x)
+        assert_array_equal(y, x)
+
+    def test_ufunc(self):
+        f = vectorize(math.cos)
+        args = np.array([0, 0.5 * np.pi, np.pi, 1.5 * np.pi, 2 * np.pi])
+        r1 = f(args)
+        r2 = np.cos(args)
+        assert_array_almost_equal(r1, r2)
+
+    def test_keywords(self):
+
+        def foo(a, b=1):
+            return a + b
+
+        f = vectorize(foo)
+        args = np.array([1, 2, 3])
+        r1 = f(args)
+        r2 = np.array([2, 3, 4])
+        assert_array_equal(r1, r2)
+        r1 = f(args, 2)
+        r2 = np.array([3, 4, 5])
+        assert_array_equal(r1, r2)
+
+    def test_keywords_with_otypes_order1(self):
+        # gh-1620: The second call of f would crash with
+        # `ValueError: invalid number of arguments`.
+        f = vectorize(_foo1, otypes=[float])
+        # We're testing the caching of ufuncs by vectorize, so the order
+        # of these function calls is an important part of the test.
+        r1 = f(np.arange(3.0), 1.0)
+        r2 = f(np.arange(3.0))
+        assert_array_equal(r1, r2)
+
+    def test_keywords_with_otypes_order2(self):
+        # gh-1620: The second call of f would crash with
+        # `ValueError: non-broadcastable output operand with shape ()
+        # doesn't match the broadcast shape (3,)`.
+        f = vectorize(_foo1, otypes=[float])
+        # We're testing the caching of ufuncs by vectorize, so the order
+        # of these function calls is an important part of the test.
+        r1 = f(np.arange(3.0))
+        r2 = f(np.arange(3.0), 1.0)
+        assert_array_equal(r1, r2)
+
+    def test_keywords_with_otypes_order3(self):
+        # gh-1620: The third call of f would crash with
+        # `ValueError: invalid number of arguments`.
+        f = vectorize(_foo1, otypes=[float])
+        # We're testing the caching of ufuncs by vectorize, so the order
+        # of these function calls is an important part of the test.
+        r1 = f(np.arange(3.0))
+        r2 = f(np.arange(3.0), y=1.0)
+        r3 = f(np.arange(3.0))
+        assert_array_equal(r1, r2)
+        assert_array_equal(r1, r3)
+
+    def test_keywords_with_otypes_several_kwd_args1(self):
+        # gh-1620 Make sure different uses of keyword arguments
+        # don't break the vectorized function.
+        f = vectorize(_foo2, otypes=[float])
+        # We're testing the caching of ufuncs by vectorize, so the order
+        # of these function calls is an important part of the test.
+        r1 = f(10.4, z=100)
+        r2 = f(10.4, y=-1)
+        r3 = f(10.4)
+        assert_equal(r1, _foo2(10.4, z=100))
+        assert_equal(r2, _foo2(10.4, y=-1))
+        assert_equal(r3, _foo2(10.4))
+
+    def test_keywords_with_otypes_several_kwd_args2(self):
+        # gh-1620 Make sure different uses of keyword arguments
+        # don't break the vectorized function.
+        f = vectorize(_foo2, otypes=[float])
+        # We're testing the caching of ufuncs by vectorize, so the order
+        # of these function calls is an important part of the test.
+        r1 = f(z=100, x=10.4, y=-1)
+        r2 = f(1, 2, 3)
+        assert_equal(r1, _foo2(z=100, x=10.4, y=-1))
+        assert_equal(r2, _foo2(1, 2, 3))
+
+    def test_keywords_no_func_code(self):
+        # This needs to test a function that has keywords but
+        # no func_code attribute, since otherwise vectorize will
+        # inspect the func_code.
+        import random
+        try:
+            vectorize(random.randrange)  # Should succeed
+        except Exception:
+            raise AssertionError()
+
+    def test_keywords2_ticket_2100(self):
+        # Test kwarg support: enhancement ticket 2100
+
+        def foo(a, b=1):
+            return a + b
+
+        f = vectorize(foo)
+        args = np.array([1, 2, 3])
+        r1 = f(a=args)
+        r2 = np.array([2, 3, 4])
+        assert_array_equal(r1, r2)
+        r1 = f(b=1, a=args)
+        assert_array_equal(r1, r2)
+        r1 = f(args, b=2)
+        r2 = np.array([3, 4, 5])
+        assert_array_equal(r1, r2)
+
+    def test_keywords3_ticket_2100(self):
+        # Test excluded with mixed positional and kwargs: ticket 2100
+        def mypolyval(x, p):
+            _p = list(p)
+            res = _p.pop(0)
+            while _p:
+                res = res * x + _p.pop(0)
+            return res
+
+        vpolyval = np.vectorize(mypolyval, excluded=['p', 1])
+        ans = [3, 6]
+        assert_array_equal(ans, vpolyval(x=[0, 1], p=[1, 2, 3]))
+        assert_array_equal(ans, vpolyval([0, 1], p=[1, 2, 3]))
+        assert_array_equal(ans, vpolyval([0, 1], [1, 2, 3]))
+
+    def test_keywords4_ticket_2100(self):
+        # Test vectorizing function with no positional args.
+        @vectorize
+        def f(**kw):
+            res = 1.0
+            for _k in kw:
+                res *= kw[_k]
+            return res
+
+        assert_array_equal(f(a=[1, 2], b=[3, 4]), [3, 8])
+
+    def test_keywords5_ticket_2100(self):
+        # Test vectorizing function with no kwargs args.
+        @vectorize
+        def f(*v):
+            return np.prod(v)
+
+        assert_array_equal(f([1, 2], [3, 4]), [3, 8])
+
+    def test_coverage1_ticket_2100(self):
+        def foo():
+            return 1
+
+        f = vectorize(foo)
+        assert_array_equal(f(), 1)
+
+    def test_assigning_docstring(self):
+        def foo(x):
+            """Original documentation"""
+            return x
+
+        f = vectorize(foo)
+        assert_equal(f.__doc__, foo.__doc__)
+
+        doc = "Provided documentation"
+        f = vectorize(foo, doc=doc)
+        assert_equal(f.__doc__, doc)
+
+    def test_UnboundMethod_ticket_1156(self):
+        # Regression test for issue 1156
+        class Foo:
+            b = 2
+
+            def bar(self, a):
+                return a ** self.b
+
+        assert_array_equal(vectorize(Foo().bar)(np.arange(9)),
+                           np.arange(9) ** 2)
+        assert_array_equal(vectorize(Foo.bar)(Foo(), np.arange(9)),
+                           np.arange(9) ** 2)
+
+    def test_execution_order_ticket_1487(self):
+        # Regression test for dependence on execution order: issue 1487
+        f1 = vectorize(lambda x: x)
+        res1a = f1(np.arange(3))
+        res1b = f1(np.arange(0.1, 3))
+        f2 = vectorize(lambda x: x)
+        res2b = f2(np.arange(0.1, 3))
+        res2a = f2(np.arange(3))
+        assert_equal(res1a, res2a)
+        assert_equal(res1b, res2b)
+
+    def test_string_ticket_1892(self):
+        # Test vectorization over strings: issue 1892.
+        f = np.vectorize(lambda x: x)
+        s = '0123456789' * 10
+        assert_equal(s, f(s))
+
+    def test_cache(self):
+        # Ensure that vectorized func called exactly once per argument.
+        _calls = [0]
+
+        @vectorize
+        def f(x):
+            _calls[0] += 1
+            return x ** 2
+
+        f.cache = True
+        x = np.arange(5)
+        assert_array_equal(f(x), x * x)
+        assert_equal(_calls[0], len(x))
+
+    def test_otypes(self):
+        f = np.vectorize(lambda x: x)
+        f.otypes = 'i'
+        x = np.arange(5)
+        assert_array_equal(f(x), x)
+
+    @pytest.mark.skip(reason='no _parse_gufunc_signature')
+    def test_parse_gufunc_signature(self):
+        assert_equal(nfb._parse_gufunc_signature('(x)->()'), ([('x',)], [()]))
+        assert_equal(nfb._parse_gufunc_signature('(x,y)->()'),
+                     ([('x', 'y')], [()]))
+        assert_equal(nfb._parse_gufunc_signature('(x),(y)->()'),
+                     ([('x',), ('y',)], [()]))
+        assert_equal(nfb._parse_gufunc_signature('(x)->(y)'),
+                     ([('x',)], [('y',)]))
+        assert_equal(nfb._parse_gufunc_signature('(x)->(y),()'),
+                     ([('x',)], [('y',), ()]))
+        assert_equal(nfb._parse_gufunc_signature('(),(a,b,c),(d)->(d,e)'),
+                     ([(), ('a', 'b', 'c'), ('d',)], [('d', 'e')]))
+
+        # Tests to check if whitespaces are ignored
+        assert_equal(nfb._parse_gufunc_signature('(x )->()'), ([('x',)], [()]))
+        assert_equal(nfb._parse_gufunc_signature('( x , y )->(  )'),
+                     ([('x', 'y')], [()]))
+        assert_equal(nfb._parse_gufunc_signature('(x),( y) ->()'),
+                     ([('x',), ('y',)], [()]))
+        assert_equal(nfb._parse_gufunc_signature('(  x)-> (y )  '),
+                     ([('x',)], [('y',)]))
+        assert_equal(nfb._parse_gufunc_signature(' (x)->( y),( )'),
+                     ([('x',)], [('y',), ()]))
+        assert_equal(nfb._parse_gufunc_signature(
+                     '(  ), ( a,  b,c )  ,(  d)   ->   (d  ,  e)'),
+                     ([(), ('a', 'b', 'c'), ('d',)], [('d', 'e')]))
+
+        with assert_raises(ValueError):
+            nfb._parse_gufunc_signature('(x)(y)->()')
+        with assert_raises(ValueError):
+            nfb._parse_gufunc_signature('(x),(y)->')
+        with assert_raises(ValueError):
+            nfb._parse_gufunc_signature('((x))->(x)')
+
+    def test_signature_simple(self):
+        def addsubtract(a, b):
+            if a > b:
+                return a - b
+            else:
+                return a + b
+
+        f = vectorize(addsubtract, signature='(),()->()')
+        r = f([0, 3, 6, 9], [1, 3, 5, 7])
+        assert_array_equal(r, [1, 6, 1, 2])
+
+    def test_signature_mean_last(self):
+        def mean(a):
+            return a.mean()
+
+        f = vectorize(mean, signature='(n)->()')
+        r = f([[1, 3], [2, 4]])
+        assert_array_equal(r, [2, 3])
+
+    def test_signature_center(self):
+        def center(a):
+            return a - a.mean()
+
+        f = vectorize(center, signature='(n)->(n)')
+        r = f([[1, 3], [2, 4]])
+        assert_array_equal(r, [[-1, 1], [-1, 1]])
+
+    def test_signature_two_outputs(self):
+        f = vectorize(lambda x: (x, x), signature='()->(),()')
+        r = f([1, 2, 3])
+        assert_(isinstance(r, tuple) and len(r) == 2)
+        assert_array_equal(r[0], [1, 2, 3])
+        assert_array_equal(r[1], [1, 2, 3])
+
+    def test_signature_outer(self):
+        f = vectorize(np.outer, signature='(a),(b)->(a,b)')
+        r = f([1, 2], [1, 2, 3])
+        assert_array_equal(r, [[1, 2, 3], [2, 4, 6]])
+
+        r = f([[[1, 2]]], [1, 2, 3])
+        assert_array_equal(r, [[[[1, 2, 3], [2, 4, 6]]]])
+
+        r = f([[1, 0], [2, 0]], [1, 2, 3])
+        assert_array_equal(r, [[[1, 2, 3], [0, 0, 0]],
+                               [[2, 4, 6], [0, 0, 0]]])
+
+        r = f([1, 2], [[1, 2, 3], [0, 0, 0]])
+        assert_array_equal(r, [[[1, 2, 3], [2, 4, 6]],
+                               [[0, 0, 0], [0, 0, 0]]])
+
+    def test_signature_computed_size(self):
+        f = vectorize(lambda x: x[:-1], signature='(n)->(m)')
+        r = f([1, 2, 3])
+        assert_array_equal(r, [1, 2])
+
+        r = f([[1, 2, 3], [2, 3, 4]])
+        assert_array_equal(r, [[1, 2], [2, 3]])
+
+    def test_signature_excluded(self):
+
+        def foo(a, b=1):
+            return a + b
+
+        f = vectorize(foo, signature='()->()', excluded={'b'})
+        assert_array_equal(f([1, 2, 3]), [2, 3, 4])
+        assert_array_equal(f([1, 2, 3], b=0), [1, 2, 3])
+
+    def test_signature_otypes(self):
+        f = vectorize(lambda x: x, signature='(n)->(n)', otypes=['float64'])
+        r = f([1, 2, 3])
+        assert_equal(r.dtype, np.dtype('float64'))
+        assert_array_equal(r, [1, 2, 3])
+
+    def test_signature_invalid_inputs(self):
+        f = vectorize(operator.add, signature='(n),(n)->(n)')
+        with assert_raises_regex(TypeError, 'wrong number of positional'):
+            f([1, 2])
+        with assert_raises_regex(
+                ValueError, 'does not have enough dimensions'):
+            f(1, 2)
+        with assert_raises_regex(
+                ValueError, 'inconsistent size for core dimension'):
+            f([1, 2], [1, 2, 3])
+
+        f = vectorize(operator.add, signature='()->()')
+        with assert_raises_regex(TypeError, 'wrong number of positional'):
+            f(1, 2)
+
+    def test_signature_invalid_outputs(self):
+
+        f = vectorize(lambda x: x[:-1], signature='(n)->(n)')
+        with assert_raises_regex(
+                ValueError, 'inconsistent size for core dimension'):
+            f([1, 2, 3])
+
+        f = vectorize(lambda x: x, signature='()->(),()')
+        with assert_raises_regex(ValueError, 'wrong number of outputs'):
+            f(1)
+
+        f = vectorize(lambda x: (x, x), signature='()->()')
+        with assert_raises_regex(ValueError, 'wrong number of outputs'):
+            f([1, 2])
+
+    def test_size_zero_output(self):
+        # see issue 5868
+        f = np.vectorize(lambda x: x)
+        x = np.zeros([0, 5], dtype=int)
+        with assert_raises_regex(ValueError, 'otypes'):
+            f(x)
+
+        f.otypes = 'i'
+        assert_array_equal(f(x), x)
+
+        f = np.vectorize(lambda x: x, signature='()->()')
+        with assert_raises_regex(ValueError, 'otypes'):
+            f(x)
+
+        f = np.vectorize(lambda x: x, signature='()->()', otypes='i')
+        assert_array_equal(f(x), x)
+
+        f = np.vectorize(lambda x: x, signature='(n)->(n)', otypes='i')
+        assert_array_equal(f(x), x)
+
+        f = np.vectorize(lambda x: x, signature='(n)->(n)')
+        assert_array_equal(f(x.T), x.T)
+
+        f = np.vectorize(lambda x: [x], signature='()->(n)', otypes='i')
+        with assert_raises_regex(ValueError, 'new output dimensions'):
+            f(x)
+
+    def test_subclasses(self):
+        class subclass(np.ndarray):
+            pass
+
+        m = np.array([[1., 0., 0.],
+                      [0., 0., 1.],
+                      [0., 1., 0.]]).view(subclass)
+        v = np.array([[1., 2., 3.], [4., 5., 6.], [7., 8., 9.]]).view(subclass)
+        # generalized (gufunc)
+        matvec = np.vectorize(np.matmul, signature='(m,m),(m)->(m)')
+        r = matvec(m, v)
+        assert_equal(type(r), subclass)
+        assert_equal(r, [[1., 3., 2.], [4., 6., 5.], [7., 9., 8.]])
+
+        # element-wise (ufunc)
+        mult = np.vectorize(lambda x, y: x*y)
+        r = mult(m, v)
+        assert_equal(type(r), subclass)
+        assert_equal(r, m * v)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestLeaks:
+    class A:
+        iters = 20
+
+        def bound(self, *args):
+            return 0
+
+        @staticmethod
+        def unbound(*args):
+            return 0
+
+    @pytest.mark.skipif(not HAS_REFCOUNT, reason="Python lacks refcounts")
+    @pytest.mark.parametrize('name, incr', [
+            ('bound', A.iters),
+            ('unbound', 0),
+            ])
+    def test_frompyfunc_leaks(self, name, incr):
+        # exposed in gh-11867 as np.vectorized, but the problem stems from
+        # frompyfunc.
+        # class.attribute = np.frompyfunc(<method>) creates a
+        # reference cycle if <method> is a bound class method. It requires a
+        # gc collection cycle to break the cycle (on CPython 3)
+        import gc
+        A_func = getattr(self.A, name)
+        gc.disable()
+        try:
+            refcount = sys.getrefcount(A_func)
+            for i in range(self.A.iters):
+                a = self.A()
+                a.f = np.frompyfunc(getattr(a, name), 1, 1)
+                out = a.f(np.arange(10))
+            a = None
+            # A.func is part of a reference cycle if incr is non-zero
+            assert_equal(sys.getrefcount(A_func), refcount + incr)
+            for i in range(5):
+                gc.collect()
+            assert_equal(sys.getrefcount(A_func), refcount)
+        finally:
+            gc.enable()
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestDigitize:
+
+    def test_forward(self):
+        x = np.arange(-6, 5)
+        bins = np.arange(-5, 5)
+        assert_array_equal(digitize(x, bins), np.arange(11))
+
+    def test_reverse(self):
+        x = np.arange(5, -6, -1)
+        bins = np.arange(5, -5, -1)
+        assert_array_equal(digitize(x, bins), np.arange(11))
+
+    def test_random(self):
+        x = rand(10)
+        bin = np.linspace(x.min(), x.max(), 10)
+        assert_(np.all(digitize(x, bin) != 0))
+
+    def test_right_basic(self):
+        x = [1, 5, 4, 10, 8, 11, 0]
+        bins = [1, 5, 10]
+        default_answer = [1, 2, 1, 3, 2, 3, 0]
+        assert_array_equal(digitize(x, bins), default_answer)
+        right_answer = [0, 1, 1, 2, 2, 3, 0]
+        assert_array_equal(digitize(x, bins, True), right_answer)
+
+    def test_right_open(self):
+        x = np.arange(-6, 5)
+        bins = np.arange(-6, 4)
+        assert_array_equal(digitize(x, bins, True), np.arange(11))
+
+    def test_right_open_reverse(self):
+        x = np.arange(5, -6, -1)
+        bins = np.arange(4, -6, -1)
+        assert_array_equal(digitize(x, bins, True), np.arange(11))
+
+    def test_right_open_random(self):
+        x = rand(10)
+        bins = np.linspace(x.min(), x.max(), 10)
+        assert_(np.all(digitize(x, bins, True) != 10))
+
+    def test_monotonic(self):
+        x = [-1, 0, 1, 2]
+        bins = [0, 0, 1]
+        assert_array_equal(digitize(x, bins, False), [0, 2, 3, 3])
+        assert_array_equal(digitize(x, bins, True), [0, 0, 2, 3])
+        bins = [1, 1, 0]
+        assert_array_equal(digitize(x, bins, False), [3, 2, 0, 0])
+        assert_array_equal(digitize(x, bins, True), [3, 3, 2, 0])
+        bins = [1, 1, 1, 1]
+        assert_array_equal(digitize(x, bins, False), [0, 0, 4, 4])
+        assert_array_equal(digitize(x, bins, True), [0, 0, 0, 4])
+        bins = [0, 0, 1, 0]
+        assert_raises(ValueError, digitize, x, bins)
+        bins = [1, 1, 0, 1]
+        assert_raises(ValueError, digitize, x, bins)
+
+    def test_casting_error(self):
+        x = [1, 2, 3 + 1.j]
+        bins = [1, 2, 3]
+        assert_raises(TypeError, digitize, x, bins)
+        x, bins = bins, x
+        assert_raises(TypeError, digitize, x, bins)
+
+    def test_return_type(self):
+        # Functions returning indices should always return base ndarrays
+        class A(np.ndarray):
+            pass
+        a = np.arange(5).view(A)
+        b = np.arange(1, 3).view(A)
+        assert_(not isinstance(digitize(b, a, False), A))
+        assert_(not isinstance(digitize(b, a, True), A))
+
+    def test_large_integers_increasing(self):
+        # gh-11022
+        x = 2**54  # loses precision in a float
+        assert_equal(np.digitize(x, [x - 1, x + 1]), 1)
+
+    @pytest.mark.xfail(
+        reason="gh-11022: np.core.multiarray._monoticity loses precision")
+    def test_large_integers_decreasing(self):
+        # gh-11022
+        x = 2**54  # loses precision in a float
+        assert_equal(np.digitize(x, [x + 1, x - 1]), 1)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestUnwrap:
+
+    def test_simple(self):
+        # check that unwrap removes jumps greater that 2*pi
+        assert_array_equal(unwrap([1, 1 + 2 * np.pi]), [1, 1])
+        # check that unwrap maintains continuity
+        assert_(np.all(diff(unwrap(rand(10) * 100)) < np.pi))
+
+    def test_period(self):
+        # check that unwrap removes jumps greater that 255
+        assert_array_equal(unwrap([1, 1 + 256], period=255), [1, 2])
+        # check that unwrap maintains continuity
+        assert_(np.all(diff(unwrap(rand(10) * 1000, period=255)) < 255))
+        # check simple case
+        simple_seq = np.array([0, 75, 150, 225, 300])
+        wrap_seq = np.mod(simple_seq, 255)
+        assert_array_equal(unwrap(wrap_seq, period=255), simple_seq)
+        # check custom discont value
+        uneven_seq = np.array([0, 75, 150, 225, 300, 430])
+        wrap_uneven = np.mod(uneven_seq, 250)
+        no_discont = unwrap(wrap_uneven, period=250)
+        assert_array_equal(no_discont, [0, 75, 150, 225, 300, 180])
+        sm_discont = unwrap(wrap_uneven, period=250, discont=140)
+        assert_array_equal(sm_discont, [0, 75, 150, 225, 300, 430])
+        assert sm_discont.dtype == wrap_uneven.dtype
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+@pytest.mark.parametrize(
+    "dtype", "O" + np.typecodes["AllInteger"] + np.typecodes["Float"]
+)
+@pytest.mark.parametrize("M", [0, 1, 10])
+class TestFilterwindows:
+
+    def test_hanning(self, dtype: str, M: int) -> None:
+        scalar = np.array(M, dtype=dtype)[()]
+
+        w = hanning(scalar)
+        if dtype == "O":
+            ref_dtype = np.float64
+        else:
+            ref_dtype = np.result_type(scalar.dtype, np.float64)
+        assert w.dtype == ref_dtype
+
+        # check symmetry
+        assert_equal(w, flipud(w))
+
+        # check known value
+        if scalar < 1:
+            assert_array_equal(w, np.array([]))
+        elif scalar == 1:
+            assert_array_equal(w, np.ones(1))
+        else:
+            assert_almost_equal(np.sum(w, axis=0), 4.500, 4)
+
+    def test_hamming(self, dtype: str, M: int) -> None:
+        scalar = np.array(M, dtype=dtype)[()]
+
+        w = hamming(scalar)
+        if dtype == "O":
+            ref_dtype = np.float64
+        else:
+            ref_dtype = np.result_type(scalar.dtype, np.float64)
+        assert w.dtype == ref_dtype
+
+        # check symmetry
+        assert_equal(w, flipud(w))
+
+        # check known value
+        if scalar < 1:
+            assert_array_equal(w, np.array([]))
+        elif scalar == 1:
+            assert_array_equal(w, np.ones(1))
+        else:
+            assert_almost_equal(np.sum(w, axis=0), 4.9400, 4)
+
+    def test_bartlett(self, dtype: str, M: int) -> None:
+        scalar = np.array(M, dtype=dtype)[()]
+
+        w = bartlett(scalar)
+        if dtype == "O":
+            ref_dtype = np.float64
+        else:
+            ref_dtype = np.result_type(scalar.dtype, np.float64)
+        assert w.dtype == ref_dtype
+
+        # check symmetry
+        assert_equal(w, flipud(w))
+
+        # check known value
+        if scalar < 1:
+            assert_array_equal(w, np.array([]))
+        elif scalar == 1:
+            assert_array_equal(w, np.ones(1))
+        else:
+            assert_almost_equal(np.sum(w, axis=0), 4.4444, 4)
+
+    def test_blackman(self, dtype: str, M: int) -> None:
+        scalar = np.array(M, dtype=dtype)[()]
+
+        w = blackman(scalar)
+        if dtype == "O":
+            ref_dtype = np.float64
+        else:
+            ref_dtype = np.result_type(scalar.dtype, np.float64)
+        assert w.dtype == ref_dtype
+
+        # check symmetry
+        assert_equal(w, flipud(w))
+
+        # check known value
+        if scalar < 1:
+            assert_array_equal(w, np.array([]))
+        elif scalar == 1:
+            assert_array_equal(w, np.ones(1))
+        else:
+            assert_almost_equal(np.sum(w, axis=0), 3.7800, 4)
+
+    def test_kaiser(self, dtype: str, M: int) -> None:
+        scalar = np.array(M, dtype=dtype)[()]
+
+        w = kaiser(scalar, 0)
+        if dtype == "O":
+            ref_dtype = np.float64
+        else:
+            ref_dtype = np.result_type(scalar.dtype, np.float64)
+        assert w.dtype == ref_dtype
+
+        # check symmetry
+        assert_equal(w, flipud(w))
+
+        # check known value
+        if scalar < 1:
+            assert_array_equal(w, np.array([]))
+        elif scalar == 1:
+            assert_array_equal(w, np.ones(1))
+        else:
+            assert_almost_equal(np.sum(w, axis=0), 10, 15)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestTrapz:
+
+    def test_simple(self):
+        x = np.arange(-10, 10, .1)
+        r = trapz(np.exp(-.5 * x ** 2) / np.sqrt(2 * np.pi), dx=0.1)
+        # check integral of normal equals 1
+        assert_almost_equal(r, 1, 7)
+
+    def test_ndim(self):
+        x = np.linspace(0, 1, 3)
+        y = np.linspace(0, 2, 8)
+        z = np.linspace(0, 3, 13)
+
+        wx = np.ones_like(x) * (x[1] - x[0])
+        wx[0] /= 2
+        wx[-1] /= 2
+        wy = np.ones_like(y) * (y[1] - y[0])
+        wy[0] /= 2
+        wy[-1] /= 2
+        wz = np.ones_like(z) * (z[1] - z[0])
+        wz[0] /= 2
+        wz[-1] /= 2
+
+        q = x[:, None, None] + y[None,:, None] + z[None, None,:]
+
+        qx = (q * wx[:, None, None]).sum(axis=0)
+        qy = (q * wy[None, :, None]).sum(axis=1)
+        qz = (q * wz[None, None, :]).sum(axis=2)
+
+        # n-d `x`
+        r = trapz(q, x=x[:, None, None], axis=0)
+        assert_almost_equal(r, qx)
+        r = trapz(q, x=y[None,:, None], axis=1)
+        assert_almost_equal(r, qy)
+        r = trapz(q, x=z[None, None,:], axis=2)
+        assert_almost_equal(r, qz)
+
+        # 1-d `x`
+        r = trapz(q, x=x, axis=0)
+        assert_almost_equal(r, qx)
+        r = trapz(q, x=y, axis=1)
+        assert_almost_equal(r, qy)
+        r = trapz(q, x=z, axis=2)
+        assert_almost_equal(r, qz)
+
+    def test_masked(self):
+        # Testing that masked arrays behave as if the function is 0 where
+        # masked
+        x = np.arange(5)
+        y = x * x
+        mask = x == 2
+        ym = np.ma.array(y, mask=mask)
+        r = 13.0  # sum(0.5 * (0 + 1) * 1.0 + 0.5 * (9 + 16))
+        assert_almost_equal(trapz(ym, x), r)
+
+        xm = np.ma.array(x, mask=mask)
+        assert_almost_equal(trapz(ym, xm), r)
+
+        xm = np.ma.array(x, mask=mask)
+        assert_almost_equal(trapz(y, xm), r)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestSinc:
+
+    def test_simple(self):
+        assert_(sinc(0) == 1)
+        w = sinc(np.linspace(-1, 1, 100))
+        # check symmetry
+        assert_array_almost_equal(w, flipud(w), 7)
+
+    def test_array_like(self):
+        x = [0, 0.5]
+        y1 = sinc(np.array(x))
+        y2 = sinc(list(x))
+        y3 = sinc(tuple(x))
+        assert_array_equal(y1, y2)
+        assert_array_equal(y1, y3)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestUnique:
+
+    def test_simple(self):
+        x = np.array([4, 3, 2, 1, 1, 2, 3, 4, 0])
+        assert_(np.all(unique(x) == [0, 1, 2, 3, 4]))
+        assert_(unique(np.array([1, 1, 1, 1, 1])) == np.array([1]))
+        x = ['widget', 'ham', 'foo', 'bar', 'foo', 'ham']
+        assert_(np.all(unique(x) == ['bar', 'foo', 'ham', 'widget']))
+        x = np.array([5 + 6j, 1 + 1j, 1 + 10j, 10, 5 + 6j])
+        assert_(np.all(unique(x) == [1 + 1j, 1 + 10j, 5 + 6j, 10]))
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestCheckFinite:
+
+    def test_simple(self):
+        a = [1, 2, 3]
+        b = [1, 2, np.inf]
+        c = [1, 2, np.nan]
+        np.lib.asarray_chkfinite(a)
+        assert_raises(ValueError, np.lib.asarray_chkfinite, b)
+        assert_raises(ValueError, np.lib.asarray_chkfinite, c)
+
+    def test_dtype_order(self):
+        # Regression test for missing dtype and order arguments
+        a = [1, 2, 3]
+        a = np.lib.asarray_chkfinite(a, order='F', dtype=np.float64)
+        assert_(a.dtype == np.float64)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestCorrCoef:
+    A = np.array(
+        [[0.15391142, 0.18045767, 0.14197213],
+         [0.70461506, 0.96474128, 0.27906989],
+         [0.9297531, 0.32296769, 0.19267156]])
+    B = np.array(
+        [[0.10377691, 0.5417086, 0.49807457],
+         [0.82872117, 0.77801674, 0.39226705],
+         [0.9314666, 0.66800209, 0.03538394]])
+    res1 = np.array(
+        [[1., 0.9379533, -0.04931983],
+         [0.9379533, 1., 0.30007991],
+         [-0.04931983, 0.30007991, 1.]])
+    res2 = np.array(
+        [[1., 0.9379533, -0.04931983, 0.30151751, 0.66318558, 0.51532523],
+         [0.9379533, 1., 0.30007991, -0.04781421, 0.88157256, 0.78052386],
+         [-0.04931983, 0.30007991, 1., -0.96717111, 0.71483595, 0.83053601],
+         [0.30151751, -0.04781421, -0.96717111, 1., -0.51366032, -0.66173113],
+         [0.66318558, 0.88157256, 0.71483595, -0.51366032, 1., 0.98317823],
+         [0.51532523, 0.78052386, 0.83053601, -0.66173113, 0.98317823, 1.]])
+
+    def test_non_array(self):
+        assert_almost_equal(np.corrcoef([0, 1, 0], [1, 0, 1]),
+                            [[1., -1.], [-1.,  1.]])
+
+    def test_simple(self):
+        tgt1 = corrcoef(self.A)
+        assert_almost_equal(tgt1, self.res1)
+        assert_(np.all(np.abs(tgt1) <= 1.0))
+
+        tgt2 = corrcoef(self.A, self.B)
+        assert_almost_equal(tgt2, self.res2)
+        assert_(np.all(np.abs(tgt2) <= 1.0))
+
+    def test_ddof(self):
+        # ddof raises DeprecationWarning
+        with suppress_warnings() as sup:
+            warnings.simplefilter("always")
+            assert_warns(DeprecationWarning, corrcoef, self.A, ddof=-1)
+            sup.filter(DeprecationWarning)
+            # ddof has no or negligible effect on the function
+            assert_almost_equal(corrcoef(self.A, ddof=-1), self.res1)
+            assert_almost_equal(corrcoef(self.A, self.B, ddof=-1), self.res2)
+            assert_almost_equal(corrcoef(self.A, ddof=3), self.res1)
+            assert_almost_equal(corrcoef(self.A, self.B, ddof=3), self.res2)
+
+    def test_bias(self):
+        # bias raises DeprecationWarning
+        with suppress_warnings() as sup:
+            warnings.simplefilter("always")
+            assert_warns(DeprecationWarning, corrcoef, self.A, self.B, 1, 0)
+            assert_warns(DeprecationWarning, corrcoef, self.A, bias=0)
+            sup.filter(DeprecationWarning)
+            # bias has no or negligible effect on the function
+            assert_almost_equal(corrcoef(self.A, bias=1), self.res1)
+
+    def test_complex(self):
+        x = np.array([[1, 2, 3], [1j, 2j, 3j]])
+        res = corrcoef(x)
+        tgt = np.array([[1., -1.j], [1.j, 1.]])
+        assert_allclose(res, tgt)
+        assert_(np.all(np.abs(res) <= 1.0))
+
+    def test_xy(self):
+        x = np.array([[1, 2, 3]])
+        y = np.array([[1j, 2j, 3j]])
+        assert_allclose(np.corrcoef(x, y), np.array([[1., -1.j], [1.j, 1.]]))
+
+    def test_empty(self):
+        with warnings.catch_warnings(record=True):
+            warnings.simplefilter('always', RuntimeWarning)
+            assert_array_equal(corrcoef(np.array([])), np.nan)
+            assert_array_equal(corrcoef(np.array([]).reshape(0, 2)),
+                               np.array([]).reshape(0, 0))
+            assert_array_equal(corrcoef(np.array([]).reshape(2, 0)),
+                               np.array([[np.nan, np.nan], [np.nan, np.nan]]))
+
+    def test_extreme(self):
+        x = [[1e-100, 1e100], [1e100, 1e-100]]
+        with np.errstate(all='raise'):
+            c = corrcoef(x)
+        assert_array_almost_equal(c, np.array([[1., -1.], [-1., 1.]]))
+        assert_(np.all(np.abs(c) <= 1.0))
+
+    @pytest.mark.parametrize("test_type", [np.half, np.single, np.double])
+    def test_corrcoef_dtype(self, test_type):
+        cast_A = self.A.astype(test_type)
+        res = corrcoef(cast_A, dtype=test_type)
+        assert test_type == res.dtype
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestCov:
+    x1 = np.array([[0, 2], [1, 1], [2, 0]]).T
+    res1 = np.array([[1., -1.], [-1., 1.]])
+    x2 = np.array([0.0, 1.0, 2.0], ndmin=2)
+    frequencies = np.array([1, 4, 1])
+    x2_repeats = np.array([[0.0], [1.0], [1.0], [1.0], [1.0], [2.0]]).T
+    res2 = np.array([[0.4, -0.4], [-0.4, 0.4]])
+    unit_frequencies = np.ones(3, dtype=np.int_)
+    weights = np.array([1.0, 4.0, 1.0])
+    res3 = np.array([[2. / 3., -2. / 3.], [-2. / 3., 2. / 3.]])
+    unit_weights = np.ones(3)
+    x3 = np.array([0.3942, 0.5969, 0.7730, 0.9918, 0.7964])
+
+    def test_basic(self):
+        assert_allclose(cov(self.x1), self.res1)
+
+    def test_complex(self):
+        x = np.array([[1, 2, 3], [1j, 2j, 3j]])
+        res = np.array([[1., -1.j], [1.j, 1.]])
+        assert_allclose(cov(x), res)
+        assert_allclose(cov(x, aweights=np.ones(3)), res)
+
+    def test_xy(self):
+        x = np.array([[1, 2, 3]])
+        y = np.array([[1j, 2j, 3j]])
+        assert_allclose(cov(x, y), np.array([[1., -1.j], [1.j, 1.]]))
+
+    def test_empty(self):
+        with warnings.catch_warnings(record=True):
+            warnings.simplefilter('always', RuntimeWarning)
+            assert_array_equal(cov(np.array([])), np.nan)
+            assert_array_equal(cov(np.array([]).reshape(0, 2)),
+                               np.array([]).reshape(0, 0))
+            assert_array_equal(cov(np.array([]).reshape(2, 0)),
+                               np.array([[np.nan, np.nan], [np.nan, np.nan]]))
+
+    def test_wrong_ddof(self):
+        with warnings.catch_warnings(record=True):
+            warnings.simplefilter('always', RuntimeWarning)
+            assert_array_equal(cov(self.x1, ddof=5),
+                               np.array([[np.inf, -np.inf],
+                                         [-np.inf, np.inf]]))
+
+    def test_1D_rowvar(self):
+        assert_allclose(cov(self.x3), cov(self.x3, rowvar=False))
+        y = np.array([0.0780, 0.3107, 0.2111, 0.0334, 0.8501])
+        assert_allclose(cov(self.x3, y), cov(self.x3, y, rowvar=False))
+
+    def test_1D_variance(self):
+        assert_allclose(cov(self.x3, ddof=1), np.var(self.x3, ddof=1))
+
+    def test_fweights(self):
+        assert_allclose(cov(self.x2, fweights=self.frequencies),
+                        cov(self.x2_repeats))
+        assert_allclose(cov(self.x1, fweights=self.frequencies),
+                        self.res2)
+        assert_allclose(cov(self.x1, fweights=self.unit_frequencies),
+                        self.res1)
+        nonint = self.frequencies + 0.5
+        assert_raises(TypeError, cov, self.x1, fweights=nonint)
+        f = np.ones((2, 3), dtype=np.int_)
+        assert_raises(RuntimeError, cov, self.x1, fweights=f)
+        f = np.ones(2, dtype=np.int_)
+        assert_raises(RuntimeError, cov, self.x1, fweights=f)
+        f = -1 * np.ones(3, dtype=np.int_)
+        assert_raises(ValueError, cov, self.x1, fweights=f)
+
+    def test_aweights(self):
+        assert_allclose(cov(self.x1, aweights=self.weights), self.res3)
+        assert_allclose(cov(self.x1, aweights=3.0 * self.weights),
+                        cov(self.x1, aweights=self.weights))
+        assert_allclose(cov(self.x1, aweights=self.unit_weights), self.res1)
+        w = np.ones((2, 3))
+        assert_raises(RuntimeError, cov, self.x1, aweights=w)
+        w = np.ones(2)
+        assert_raises(RuntimeError, cov, self.x1, aweights=w)
+        w = -1.0 * np.ones(3)
+        assert_raises(ValueError, cov, self.x1, aweights=w)
+
+    def test_unit_fweights_and_aweights(self):
+        assert_allclose(cov(self.x2, fweights=self.frequencies,
+                            aweights=self.unit_weights),
+                        cov(self.x2_repeats))
+        assert_allclose(cov(self.x1, fweights=self.frequencies,
+                            aweights=self.unit_weights),
+                        self.res2)
+        assert_allclose(cov(self.x1, fweights=self.unit_frequencies,
+                            aweights=self.unit_weights),
+                        self.res1)
+        assert_allclose(cov(self.x1, fweights=self.unit_frequencies,
+                            aweights=self.weights),
+                        self.res3)
+        assert_allclose(cov(self.x1, fweights=self.unit_frequencies,
+                            aweights=3.0 * self.weights),
+                        cov(self.x1, aweights=self.weights))
+        assert_allclose(cov(self.x1, fweights=self.unit_frequencies,
+                            aweights=self.unit_weights),
+                        self.res1)
+
+    @pytest.mark.parametrize("test_type", [np.half, np.single, np.double])
+    def test_cov_dtype(self, test_type):
+        cast_x1 = self.x1.astype(test_type)
+        res = cov(cast_x1, dtype=test_type)
+        assert test_type == res.dtype
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class Test_I0:
+
+    def test_simple(self):
+        assert_almost_equal(
+            i0(0.5),
+            np.array(1.0634833707413234))
+
+        # need at least one test above 8, as the implementation is piecewise
+        A = np.array([0.49842636, 0.6969809, 0.22011976, 0.0155549, 10.0])
+        expected = np.array([1.06307822, 1.12518299, 1.01214991, 1.00006049, 2815.71662847])
+        assert_almost_equal(i0(A), expected)
+        assert_almost_equal(i0(-A), expected)
+
+        B = np.array([[0.827002, 0.99959078],
+                      [0.89694769, 0.39298162],
+                      [0.37954418, 0.05206293],
+                      [0.36465447, 0.72446427],
+                      [0.48164949, 0.50324519]])
+        assert_almost_equal(
+            i0(B),
+            np.array([[1.17843223, 1.26583466],
+                      [1.21147086, 1.03898290],
+                      [1.03633899, 1.00067775],
+                      [1.03352052, 1.13557954],
+                      [1.05884290, 1.06432317]]))
+        # Regression test for gh-11205
+        i0_0 = np.i0([0.])
+        assert_equal(i0_0.shape, (1,))
+        assert_array_equal(np.i0([0.]), np.array([1.]))
+
+    def test_non_array(self):
+        a = np.arange(4)
+
+        class array_like:
+            __array_interface__ = a.__array_interface__
+
+            def __array_wrap__(self, arr):
+                return self
+
+        # E.g. pandas series survive ufunc calls through array-wrap:
+        assert isinstance(np.abs(array_like()), array_like)
+        exp = np.i0(a)
+        res = np.i0(array_like())
+
+        assert_array_equal(exp, res)
+
+    def test_complex(self):
+        a = np.array([0, 1 + 2j])
+        with pytest.raises(TypeError, match="i0 not supported for complex values"):
+            res = i0(a)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestKaiser:
+
+    def test_simple(self):
+        assert_(np.isfinite(kaiser(1, 1.0)))
+        assert_almost_equal(kaiser(0, 1.0),
+                            np.array([]))
+        assert_almost_equal(kaiser(2, 1.0),
+                            np.array([0.78984831, 0.78984831]))
+        assert_almost_equal(kaiser(5, 1.0),
+                            np.array([0.78984831, 0.94503323, 1.,
+                                      0.94503323, 0.78984831]))
+        assert_almost_equal(kaiser(5, 1.56789),
+                            np.array([0.58285404, 0.88409679, 1.,
+                                      0.88409679, 0.58285404]))
+
+    def test_int_beta(self):
+        kaiser(3, 4)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestMsort:
+
+    def test_simple(self):
+        A = np.array([[0.44567325, 0.79115165, 0.54900530],
+                      [0.36844147, 0.37325583, 0.96098397],
+                      [0.64864341, 0.52929049, 0.39172155]])
+        with pytest.warns(DeprecationWarning, match="msort is deprecated"):
+            assert_almost_equal(
+                msort(A),
+                np.array([[0.36844147, 0.37325583, 0.39172155],
+                          [0.44567325, 0.52929049, 0.54900530],
+                          [0.64864341, 0.79115165, 0.96098397]]))
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestMeshgrid:
+
+    def test_simple(self):
+        [X, Y] = meshgrid([1, 2, 3], [4, 5, 6, 7])
+        assert_array_equal(X, np.array([[1, 2, 3],
+                                        [1, 2, 3],
+                                        [1, 2, 3],
+                                        [1, 2, 3]]))
+        assert_array_equal(Y, np.array([[4, 4, 4],
+                                        [5, 5, 5],
+                                        [6, 6, 6],
+                                        [7, 7, 7]]))
+
+    def test_single_input(self):
+        [X] = meshgrid([1, 2, 3, 4])
+        assert_array_equal(X, np.array([1, 2, 3, 4]))
+
+    def test_no_input(self):
+        args = []
+        assert_array_equal([], meshgrid(*args))
+        assert_array_equal([], meshgrid(*args, copy=False))
+
+    def test_indexing(self):
+        x = [1, 2, 3]
+        y = [4, 5, 6, 7]
+        [X, Y] = meshgrid(x, y, indexing='ij')
+        assert_array_equal(X, np.array([[1, 1, 1, 1],
+                                        [2, 2, 2, 2],
+                                        [3, 3, 3, 3]]))
+        assert_array_equal(Y, np.array([[4, 5, 6, 7],
+                                        [4, 5, 6, 7],
+                                        [4, 5, 6, 7]]))
+
+        # Test expected shapes:
+        z = [8, 9]
+        assert_(meshgrid(x, y)[0].shape == (4, 3))
+        assert_(meshgrid(x, y, indexing='ij')[0].shape == (3, 4))
+        assert_(meshgrid(x, y, z)[0].shape == (4, 3, 2))
+        assert_(meshgrid(x, y, z, indexing='ij')[0].shape == (3, 4, 2))
+
+        assert_raises(ValueError, meshgrid, x, y, indexing='notvalid')
+
+    def test_sparse(self):
+        [X, Y] = meshgrid([1, 2, 3], [4, 5, 6, 7], sparse=True)
+        assert_array_equal(X, np.array([[1, 2, 3]]))
+        assert_array_equal(Y, np.array([[4], [5], [6], [7]]))
+
+    def test_invalid_arguments(self):
+        # Test that meshgrid complains about invalid arguments
+        # Regression test for issue #4755:
+        # https://github.com/numpy/numpy/issues/4755
+        assert_raises(TypeError, meshgrid,
+                      [1, 2, 3], [4, 5, 6, 7], indices='ij')
+
+    def test_return_type(self):
+        # Test for appropriate dtype in returned arrays.
+        # Regression test for issue #5297
+        # https://github.com/numpy/numpy/issues/5297
+        x = np.arange(0, 10, dtype=np.float32)
+        y = np.arange(10, 20, dtype=np.float64)
+
+        X, Y = np.meshgrid(x,y)
+
+        assert_(X.dtype == x.dtype)
+        assert_(Y.dtype == y.dtype)
+
+        # copy
+        X, Y = np.meshgrid(x,y, copy=True)
+
+        assert_(X.dtype == x.dtype)
+        assert_(Y.dtype == y.dtype)
+
+        # sparse
+        X, Y = np.meshgrid(x,y, sparse=True)
+
+        assert_(X.dtype == x.dtype)
+        assert_(Y.dtype == y.dtype)
+
+    def test_writeback(self):
+        # Issue 8561
+        X = np.array([1.1, 2.2])
+        Y = np.array([3.3, 4.4])
+        x, y = np.meshgrid(X, Y, sparse=False, copy=True)
+
+        x[0, :] = 0
+        assert_equal(x[0, :], 0)
+        assert_equal(x[1, :], X)
+
+    def test_nd_shape(self):
+        a, b, c, d, e = np.meshgrid(*([0] * i for i in range(1, 6)))
+        expected_shape = (2, 1, 3, 4, 5)
+        assert_equal(a.shape, expected_shape)
+        assert_equal(b.shape, expected_shape)
+        assert_equal(c.shape, expected_shape)
+        assert_equal(d.shape, expected_shape)
+        assert_equal(e.shape, expected_shape)
+
+    def test_nd_values(self):
+        a, b, c = np.meshgrid([0], [1, 2], [3, 4, 5])
+        assert_equal(a, [[[0, 0, 0]], [[0, 0, 0]]])
+        assert_equal(b, [[[1, 1, 1]], [[2, 2, 2]]])
+        assert_equal(c, [[[3, 4, 5]], [[3, 4, 5]]])
+
+    def test_nd_indexing(self):
+        a, b, c = np.meshgrid([0], [1, 2], [3, 4, 5], indexing='ij')
+        assert_equal(a, [[[0, 0, 0], [0, 0, 0]]])
+        assert_equal(b, [[[1, 1, 1], [2, 2, 2]]])
+        assert_equal(c, [[[3, 4, 5], [3, 4, 5]]])
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestPiecewise:
+
+    def test_simple(self):
+        # Condition is single bool list
+        x = piecewise([0, 0], [True, False], [1])
+        assert_array_equal(x, [1, 0])
+
+        # List of conditions: single bool list
+        x = piecewise([0, 0], [[True, False]], [1])
+        assert_array_equal(x, [1, 0])
+
+        # Conditions is single bool array
+        x = piecewise([0, 0], np.array([True, False]), [1])
+        assert_array_equal(x, [1, 0])
+
+        # Condition is single int array
+        x = piecewise([0, 0], np.array([1, 0]), [1])
+        assert_array_equal(x, [1, 0])
+
+        # List of conditions: int array
+        x = piecewise([0, 0], [np.array([1, 0])], [1])
+        assert_array_equal(x, [1, 0])
+
+        x = piecewise([0, 0], [[False, True]], [lambda x:-1])
+        assert_array_equal(x, [0, -1])
+
+        assert_raises_regex(ValueError, '1 or 2 functions are expected',
+            piecewise, [0, 0], [[False, True]], [])
+        assert_raises_regex(ValueError, '1 or 2 functions are expected',
+            piecewise, [0, 0], [[False, True]], [1, 2, 3])
+
+    def test_two_conditions(self):
+        x = piecewise([1, 2], [[True, False], [False, True]], [3, 4])
+        assert_array_equal(x, [3, 4])
+
+    def test_scalar_domains_three_conditions(self):
+        x = piecewise(3, [True, False, False], [4, 2, 0])
+        assert_equal(x, 4)
+
+    def test_default(self):
+        # No value specified for x[1], should be 0
+        x = piecewise([1, 2], [True, False], [2])
+        assert_array_equal(x, [2, 0])
+
+        # Should set x[1] to 3
+        x = piecewise([1, 2], [True, False], [2, 3])
+        assert_array_equal(x, [2, 3])
+
+    def test_0d(self):
+        x = np.array(3)
+        y = piecewise(x, x > 3, [4, 0])
+        assert_(y.ndim == 0)
+        assert_(y == 0)
+
+        x = 5
+        y = piecewise(x, [True, False], [1, 0])
+        assert_(y.ndim == 0)
+        assert_(y == 1)
+
+        # With 3 ranges (It was failing, before)
+        y = piecewise(x, [False, False, True], [1, 2, 3])
+        assert_array_equal(y, 3)
+
+    def test_0d_comparison(self):
+        x = 3
+        y = piecewise(x, [x <= 3, x > 3], [4, 0])  # Should succeed.
+        assert_equal(y, 4)
+
+        # With 3 ranges (It was failing, before)
+        x = 4
+        y = piecewise(x, [x <= 3, (x > 3) * (x <= 5), x > 5], [1, 2, 3])
+        assert_array_equal(y, 2)
+
+        assert_raises_regex(ValueError, '2 or 3 functions are expected',
+            piecewise, x, [x <= 3, x > 3], [1])
+        assert_raises_regex(ValueError, '2 or 3 functions are expected',
+            piecewise, x, [x <= 3, x > 3], [1, 1, 1, 1])
+
+    def test_0d_0d_condition(self):
+        x = np.array(3)
+        c = np.array(x > 3)
+        y = piecewise(x, [c], [1, 2])
+        assert_equal(y, 2)
+
+    def test_multidimensional_extrafunc(self):
+        x = np.array([[-2.5, -1.5, -0.5],
+                      [0.5, 1.5, 2.5]])
+        y = piecewise(x, [x < 0, x >= 2], [-1, 1, 3])
+        assert_array_equal(y, np.array([[-1., -1., -1.],
+                                        [3., 3., 1.]]))
+
+    def test_subclasses(self):
+        class subclass(np.ndarray):
+            pass
+        x = np.arange(5.).view(subclass)
+        r = piecewise(x, [x<2., x>=4], [-1., 1., 0.])
+        assert_equal(type(r), subclass)
+        assert_equal(r, [-1., -1., 0., 0., 1.])
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestBincount:
+
+    def test_simple(self):
+        y = np.bincount(np.arange(4))
+        assert_array_equal(y, np.ones(4))
+
+    def test_simple2(self):
+        y = np.bincount(np.array([1, 5, 2, 4, 1]))
+        assert_array_equal(y, np.array([0, 2, 1, 0, 1, 1]))
+
+    def test_simple_weight(self):
+        x = np.arange(4)
+        w = np.array([0.2, 0.3, 0.5, 0.1])
+        y = np.bincount(x, w)
+        assert_array_equal(y, w)
+
+    def test_simple_weight2(self):
+        x = np.array([1, 2, 4, 5, 2])
+        w = np.array([0.2, 0.3, 0.5, 0.1, 0.2])
+        y = np.bincount(x, w)
+        assert_array_equal(y, np.array([0, 0.2, 0.5, 0, 0.5, 0.1]))
+
+    def test_with_minlength(self):
+        x = np.array([0, 1, 0, 1, 1])
+        y = np.bincount(x, minlength=3)
+        assert_array_equal(y, np.array([2, 3, 0]))
+        x = []
+        y = np.bincount(x, minlength=0)
+        assert_array_equal(y, np.array([]))
+
+    def test_with_minlength_smaller_than_maxvalue(self):
+        x = np.array([0, 1, 1, 2, 2, 3, 3])
+        y = np.bincount(x, minlength=2)
+        assert_array_equal(y, np.array([1, 2, 2, 2]))
+        y = np.bincount(x, minlength=0)
+        assert_array_equal(y, np.array([1, 2, 2, 2]))
+
+    def test_with_minlength_and_weights(self):
+        x = np.array([1, 2, 4, 5, 2])
+        w = np.array([0.2, 0.3, 0.5, 0.1, 0.2])
+        y = np.bincount(x, w, 8)
+        assert_array_equal(y, np.array([0, 0.2, 0.5, 0, 0.5, 0.1, 0, 0]))
+
+    def test_empty(self):
+        x = np.array([], dtype=int)
+        y = np.bincount(x)
+        assert_array_equal(x, y)
+
+    def test_empty_with_minlength(self):
+        x = np.array([], dtype=int)
+        y = np.bincount(x, minlength=5)
+        assert_array_equal(y, np.zeros(5, dtype=int))
+
+    def test_with_incorrect_minlength(self):
+        x = np.array([], dtype=int)
+        assert_raises_regex(TypeError,
+                            "'str' object cannot be interpreted",
+                            lambda: np.bincount(x, minlength="foobar"))
+        assert_raises_regex(ValueError,
+                            "must not be negative",
+                            lambda: np.bincount(x, minlength=-1))
+
+        x = np.arange(5)
+        assert_raises_regex(TypeError,
+                            "'str' object cannot be interpreted",
+                            lambda: np.bincount(x, minlength="foobar"))
+        assert_raises_regex(ValueError,
+                            "must not be negative",
+                            lambda: np.bincount(x, minlength=-1))
+
+    @pytest.mark.skipif(not HAS_REFCOUNT, reason="Python lacks refcounts")
+    def test_dtype_reference_leaks(self):
+        # gh-6805
+        intp_refcount = sys.getrefcount(np.dtype(np.intp))
+        double_refcount = sys.getrefcount(np.dtype(np.double))
+
+        for j in range(10):
+            np.bincount([1, 2, 3])
+        assert_equal(sys.getrefcount(np.dtype(np.intp)), intp_refcount)
+        assert_equal(sys.getrefcount(np.dtype(np.double)), double_refcount)
+
+        for j in range(10):
+            np.bincount([1, 2, 3], [4, 5, 6])
+        assert_equal(sys.getrefcount(np.dtype(np.intp)), intp_refcount)
+        assert_equal(sys.getrefcount(np.dtype(np.double)), double_refcount)
+
+    @pytest.mark.parametrize("vals", [[[2, 2]], 2])
+    def test_error_not_1d(self, vals):
+        # Test that values has to be 1-D (both as array and nested list)
+        vals_arr = np.asarray(vals)
+        with assert_raises(ValueError):
+            np.bincount(vals_arr)
+        with assert_raises(ValueError):
+            np.bincount(vals)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestInterp:
+
+    def test_exceptions(self):
+        assert_raises(ValueError, interp, 0, [], [])
+        assert_raises(ValueError, interp, 0, [0], [1, 2])
+        assert_raises(ValueError, interp, 0, [0, 1], [1, 2], period=0)
+        assert_raises(ValueError, interp, 0, [], [], period=360)
+        assert_raises(ValueError, interp, 0, [0], [1, 2], period=360)
+
+    def test_basic(self):
+        x = np.linspace(0, 1, 5)
+        y = np.linspace(0, 1, 5)
+        x0 = np.linspace(0, 1, 50)
+        assert_almost_equal(np.interp(x0, x, y), x0)
+
+    def test_right_left_behavior(self):
+        # Needs range of sizes to test different code paths.
+        # size ==1 is special cased, 1 < size < 5 is linear search, and
+        # size >= 5 goes through local search and possibly binary search.
+        for size in range(1, 10):
+            xp = np.arange(size, dtype=np.double)
+            yp = np.ones(size, dtype=np.double)
+            incpts = np.array([-1, 0, size - 1, size], dtype=np.double)
+            decpts = incpts[::-1]
+
+            incres = interp(incpts, xp, yp)
+            decres = interp(decpts, xp, yp)
+            inctgt = np.array([1, 1, 1, 1], dtype=float)
+            dectgt = inctgt[::-1]
+            assert_equal(incres, inctgt)
+            assert_equal(decres, dectgt)
+
+            incres = interp(incpts, xp, yp, left=0)
+            decres = interp(decpts, xp, yp, left=0)
+            inctgt = np.array([0, 1, 1, 1], dtype=float)
+            dectgt = inctgt[::-1]
+            assert_equal(incres, inctgt)
+            assert_equal(decres, dectgt)
+
+            incres = interp(incpts, xp, yp, right=2)
+            decres = interp(decpts, xp, yp, right=2)
+            inctgt = np.array([1, 1, 1, 2], dtype=float)
+            dectgt = inctgt[::-1]
+            assert_equal(incres, inctgt)
+            assert_equal(decres, dectgt)
+
+            incres = interp(incpts, xp, yp, left=0, right=2)
+            decres = interp(decpts, xp, yp, left=0, right=2)
+            inctgt = np.array([0, 1, 1, 2], dtype=float)
+            dectgt = inctgt[::-1]
+            assert_equal(incres, inctgt)
+            assert_equal(decres, dectgt)
+
+    def test_scalar_interpolation_point(self):
+        x = np.linspace(0, 1, 5)
+        y = np.linspace(0, 1, 5)
+        x0 = 0
+        assert_almost_equal(np.interp(x0, x, y), x0)
+        x0 = .3
+        assert_almost_equal(np.interp(x0, x, y), x0)
+        x0 = np.float32(.3)
+        assert_almost_equal(np.interp(x0, x, y), x0)
+        x0 = np.float64(.3)
+        assert_almost_equal(np.interp(x0, x, y), x0)
+        x0 = np.nan
+        assert_almost_equal(np.interp(x0, x, y), x0)
+
+    def test_non_finite_behavior_exact_x(self):
+        x = [1, 2, 2.5, 3, 4]
+        xp = [1, 2, 3, 4]
+        fp = [1, 2, np.inf, 4]
+        assert_almost_equal(np.interp(x, xp, fp), [1, 2, np.inf, np.inf, 4])
+        fp = [1, 2, np.nan, 4]
+        assert_almost_equal(np.interp(x, xp, fp), [1, 2, np.nan, np.nan, 4])
+
+    @pytest.fixture(params=[
+        lambda x: np.float_(x),
+        lambda x: _make_complex(x, 0),
+        lambda x: _make_complex(0, x),
+        lambda x: _make_complex(x, np.multiply(x, -2))
+    ], ids=[
+        'real',
+        'complex-real',
+        'complex-imag',
+        'complex-both'
+    ])
+    def sc(self, request):
+        """ scale function used by the below tests """
+        return request.param
+
+    def test_non_finite_any_nan(self, sc):
+        """ test that nans are propagated """
+        assert_equal(np.interp(0.5, [np.nan,      1], sc([     0,     10])), sc(np.nan))
+        assert_equal(np.interp(0.5, [     0, np.nan], sc([     0,     10])), sc(np.nan))
+        assert_equal(np.interp(0.5, [     0,      1], sc([np.nan,     10])), sc(np.nan))
+        assert_equal(np.interp(0.5, [     0,      1], sc([     0, np.nan])), sc(np.nan))
+
+    def test_non_finite_inf(self, sc):
+        """ Test that interp between opposite infs gives nan """
+        assert_equal(np.interp(0.5, [-np.inf, +np.inf], sc([      0,      10])), sc(np.nan))
+        assert_equal(np.interp(0.5, [      0,       1], sc([-np.inf, +np.inf])), sc(np.nan))
+        assert_equal(np.interp(0.5, [      0,       1], sc([+np.inf, -np.inf])), sc(np.nan))
+
+        # unless the y values are equal
+        assert_equal(np.interp(0.5, [-np.inf, +np.inf], sc([     10,      10])), sc(10))
+
+    def test_non_finite_half_inf_xf(self, sc):
+        """ Test that interp where both axes have a bound at inf gives nan """
+        assert_equal(np.interp(0.5, [-np.inf,       1], sc([-np.inf,      10])), sc(np.nan))
+        assert_equal(np.interp(0.5, [-np.inf,       1], sc([+np.inf,      10])), sc(np.nan))
+        assert_equal(np.interp(0.5, [-np.inf,       1], sc([      0, -np.inf])), sc(np.nan))
+        assert_equal(np.interp(0.5, [-np.inf,       1], sc([      0, +np.inf])), sc(np.nan))
+        assert_equal(np.interp(0.5, [      0, +np.inf], sc([-np.inf,      10])), sc(np.nan))
+        assert_equal(np.interp(0.5, [      0, +np.inf], sc([+np.inf,      10])), sc(np.nan))
+        assert_equal(np.interp(0.5, [      0, +np.inf], sc([      0, -np.inf])), sc(np.nan))
+        assert_equal(np.interp(0.5, [      0, +np.inf], sc([      0, +np.inf])), sc(np.nan))
+
+    def test_non_finite_half_inf_x(self, sc):
+        """ Test interp where the x axis has a bound at inf """
+        assert_equal(np.interp(0.5, [-np.inf, -np.inf], sc([0, 10])), sc(10))
+        assert_equal(np.interp(0.5, [-np.inf, 1      ], sc([0, 10])), sc(10))
+        assert_equal(np.interp(0.5, [      0, +np.inf], sc([0, 10])), sc(0))
+        assert_equal(np.interp(0.5, [+np.inf, +np.inf], sc([0, 10])), sc(0))
+
+    def test_non_finite_half_inf_f(self, sc):
+        """ Test interp where the f axis has a bound at inf """
+        assert_equal(np.interp(0.5, [0, 1], sc([      0, -np.inf])), sc(-np.inf))
+        assert_equal(np.interp(0.5, [0, 1], sc([      0, +np.inf])), sc(+np.inf))
+        assert_equal(np.interp(0.5, [0, 1], sc([-np.inf,      10])), sc(-np.inf))
+        assert_equal(np.interp(0.5, [0, 1], sc([+np.inf,      10])), sc(+np.inf))
+        assert_equal(np.interp(0.5, [0, 1], sc([-np.inf, -np.inf])), sc(-np.inf))
+        assert_equal(np.interp(0.5, [0, 1], sc([+np.inf, +np.inf])), sc(+np.inf))
+
+    def test_complex_interp(self):
+        # test complex interpolation
+        x = np.linspace(0, 1, 5)
+        y = np.linspace(0, 1, 5) + (1 + np.linspace(0, 1, 5))*1.0j
+        x0 = 0.3
+        y0 = x0 + (1+x0)*1.0j
+        assert_almost_equal(np.interp(x0, x, y), y0)
+        # test complex left and right
+        x0 = -1
+        left = 2 + 3.0j
+        assert_almost_equal(np.interp(x0, x, y, left=left), left)
+        x0 = 2.0
+        right = 2 + 3.0j
+        assert_almost_equal(np.interp(x0, x, y, right=right), right)
+        # test complex non finite
+        x = [1, 2, 2.5, 3, 4]
+        xp = [1, 2, 3, 4]
+        fp = [1, 2+1j, np.inf, 4]
+        y = [1, 2+1j, np.inf+0.5j, np.inf, 4]
+        assert_almost_equal(np.interp(x, xp, fp), y)
+        # test complex periodic
+        x = [-180, -170, -185, 185, -10, -5, 0, 365]
+        xp = [190, -190, 350, -350]
+        fp = [5+1.0j, 10+2j, 3+3j, 4+4j]
+        y = [7.5+1.5j, 5.+1.0j, 8.75+1.75j, 6.25+1.25j, 3.+3j, 3.25+3.25j,
+             3.5+3.5j, 3.75+3.75j]
+        assert_almost_equal(np.interp(x, xp, fp, period=360), y)
+
+    def test_zero_dimensional_interpolation_point(self):
+        x = np.linspace(0, 1, 5)
+        y = np.linspace(0, 1, 5)
+        x0 = np.array(.3)
+        assert_almost_equal(np.interp(x0, x, y), x0)
+
+        xp = np.array([0, 2, 4])
+        fp = np.array([1, -1, 1])
+
+        actual = np.interp(np.array(1), xp, fp)
+        assert_equal(actual, 0)
+        assert_(isinstance(actual, np.float64))
+
+        actual = np.interp(np.array(4.5), xp, fp, period=4)
+        assert_equal(actual, 0.5)
+        assert_(isinstance(actual, np.float64))
+
+    def test_if_len_x_is_small(self):
+        xp = np.arange(0, 10, 0.0001)
+        fp = np.sin(xp)
+        assert_almost_equal(np.interp(np.pi, xp, fp), 0.0)
+
+    def test_period(self):
+        x = [-180, -170, -185, 185, -10, -5, 0, 365]
+        xp = [190, -190, 350, -350]
+        fp = [5, 10, 3, 4]
+        y = [7.5, 5., 8.75, 6.25, 3., 3.25, 3.5, 3.75]
+        assert_almost_equal(np.interp(x, xp, fp, period=360), y)
+        x = np.array(x, order='F').reshape(2, -1)
+        y = np.array(y, order='C').reshape(2, -1)
+        assert_almost_equal(np.interp(x, xp, fp, period=360), y)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestPercentile:
+
+    def test_basic(self):
+        x = np.arange(8) * 0.5
+        assert_equal(np.percentile(x, 0), 0.)
+        assert_equal(np.percentile(x, 100), 3.5)
+        assert_equal(np.percentile(x, 50), 1.75)
+        x[1] = np.nan
+        assert_equal(np.percentile(x, 0), np.nan)
+        assert_equal(np.percentile(x, 0, method='nearest'), np.nan)
+
+    def test_fraction(self):
+        x = [Fraction(i, 2) for i in range(8)]
+
+        p = np.percentile(x, Fraction(0))
+        assert_equal(p, Fraction(0))
+        assert_equal(type(p), Fraction)
+
+        p = np.percentile(x, Fraction(100))
+        assert_equal(p, Fraction(7, 2))
+        assert_equal(type(p), Fraction)
+
+        p = np.percentile(x, Fraction(50))
+        assert_equal(p, Fraction(7, 4))
+        assert_equal(type(p), Fraction)
+
+        p = np.percentile(x, [Fraction(50)])
+        assert_equal(p, np.array([Fraction(7, 4)]))
+        assert_equal(type(p), np.ndarray)
+
+    def test_api(self):
+        d = np.ones(5)
+        np.percentile(d, 5, None, None, False)
+        np.percentile(d, 5, None, None, False, 'linear')
+        o = np.ones((1,))
+        np.percentile(d, 5, None, o, False, 'linear')
+
+    def test_complex(self):
+        arr_c = np.array([0.5+3.0j, 2.1+0.5j, 1.6+2.3j], dtype='G')
+        assert_raises(TypeError, np.percentile, arr_c, 0.5)
+        arr_c = np.array([0.5+3.0j, 2.1+0.5j, 1.6+2.3j], dtype='D')
+        assert_raises(TypeError, np.percentile, arr_c, 0.5)
+        arr_c = np.array([0.5+3.0j, 2.1+0.5j, 1.6+2.3j], dtype='F')
+        assert_raises(TypeError, np.percentile, arr_c, 0.5)
+
+    def test_2D(self):
+        x = np.array([[1, 1, 1],
+                      [1, 1, 1],
+                      [4, 4, 3],
+                      [1, 1, 1],
+                      [1, 1, 1]])
+        assert_array_equal(np.percentile(x, 50, axis=0), [1, 1, 1])
+
+    @pytest.mark.parametrize("dtype", np.typecodes["Float"])
+    def test_linear_nan_1D(self, dtype):
+        # METHOD 1 of H&F
+        arr = np.asarray([15.0, np.NAN, 35.0, 40.0, 50.0], dtype=dtype)
+        res = np.percentile(
+            arr,
+            40.0,
+            method="linear")
+        np.testing.assert_equal(res, np.NAN)
+        np.testing.assert_equal(res.dtype, arr.dtype)
+
+    H_F_TYPE_CODES = [(int_type, np.float64)
+                      for int_type in np.typecodes["AllInteger"]
+                      ] + [(np.float16, np.float16),
+                           (np.float32, np.float32),
+                           (np.float64, np.float64),
+                           ]
+
+    @pytest.mark.parametrize(["input_dtype", "expected_dtype"], H_F_TYPE_CODES)
+    @pytest.mark.parametrize(["method", "expected"],
+                             [("inverted_cdf", 20),
+                              ("averaged_inverted_cdf", 27.5),
+                              ("closest_observation", 20),
+                              ("interpolated_inverted_cdf", 20),
+                              ("hazen", 27.5),
+                              ("weibull", 26),
+                              ("linear", 29),
+                              ("median_unbiased", 27),
+                              ("normal_unbiased", 27.125),
+                              ])
+    def test_linear_interpolation(self,
+                                  method,
+                                  expected,
+                                  input_dtype,
+                                  expected_dtype):
+        expected_dtype = np.dtype(expected_dtype)
+        if np._get_promotion_state() == "legacy":
+            expected_dtype = np.promote_types(expected_dtype, np.float64)
+
+        arr = np.asarray([15.0, 20.0, 35.0, 40.0, 50.0], dtype=input_dtype)
+        actual = np.percentile(arr, 40.0, method=method)
+
+        np.testing.assert_almost_equal(
+            actual, expected_dtype.type(expected), 14)
+
+        if method in ["inverted_cdf", "closest_observation"]:
+            if input_dtype == "O":
+                np.testing.assert_equal(np.asarray(actual).dtype, np.float64)
+            else:
+                np.testing.assert_equal(np.asarray(actual).dtype,
+                                        np.dtype(input_dtype))
+        else:
+            np.testing.assert_equal(np.asarray(actual).dtype,
+                                    np.dtype(expected_dtype))
+
+    TYPE_CODES = np.typecodes["AllInteger"] + np.typecodes["Float"] + "O"
+
+    @pytest.mark.parametrize("dtype", TYPE_CODES)
+    def test_lower_higher(self, dtype):
+        assert_equal(np.percentile(np.arange(10, dtype=dtype), 50,
+                                   method='lower'), 4)
+        assert_equal(np.percentile(np.arange(10, dtype=dtype), 50,
+                                   method='higher'), 5)
+
+    @pytest.mark.parametrize("dtype", TYPE_CODES)
+    def test_midpoint(self, dtype):
+        assert_equal(np.percentile(np.arange(10, dtype=dtype), 51,
+                                   method='midpoint'), 4.5)
+        assert_equal(np.percentile(np.arange(9, dtype=dtype) + 1, 50,
+                                   method='midpoint'), 5)
+        assert_equal(np.percentile(np.arange(11, dtype=dtype), 51,
+                                   method='midpoint'), 5.5)
+        assert_equal(np.percentile(np.arange(11, dtype=dtype), 50,
+                                   method='midpoint'), 5)
+
+    @pytest.mark.parametrize("dtype", TYPE_CODES)
+    def test_nearest(self, dtype):
+        assert_equal(np.percentile(np.arange(10, dtype=dtype), 51,
+                                   method='nearest'), 5)
+        assert_equal(np.percentile(np.arange(10, dtype=dtype), 49,
+                                   method='nearest'), 4)
+
+    def test_linear_interpolation_extrapolation(self):
+        arr = np.random.rand(5)
+
+        actual = np.percentile(arr, 100)
+        np.testing.assert_equal(actual, arr.max())
+
+        actual = np.percentile(arr, 0)
+        np.testing.assert_equal(actual, arr.min())
+
+    def test_sequence(self):
+        x = np.arange(8) * 0.5
+        assert_equal(np.percentile(x, [0, 100, 50]), [0, 3.5, 1.75])
+
+    def test_axis(self):
+        x = np.arange(12).reshape(3, 4)
+
+        assert_equal(np.percentile(x, (25, 50, 100)), [2.75, 5.5, 11.0])
+
+        r0 = [[2, 3, 4, 5], [4, 5, 6, 7], [8, 9, 10, 11]]
+        assert_equal(np.percentile(x, (25, 50, 100), axis=0), r0)
+
+        r1 = [[0.75, 1.5, 3], [4.75, 5.5, 7], [8.75, 9.5, 11]]
+        assert_equal(np.percentile(x, (25, 50, 100), axis=1), np.array(r1).T)
+
+        # ensure qth axis is always first as with np.array(old_percentile(..))
+        x = np.arange(3 * 4 * 5 * 6).reshape(3, 4, 5, 6)
+        assert_equal(np.percentile(x, (25, 50)).shape, (2,))
+        assert_equal(np.percentile(x, (25, 50, 75)).shape, (3,))
+        assert_equal(np.percentile(x, (25, 50), axis=0).shape, (2, 4, 5, 6))
+        assert_equal(np.percentile(x, (25, 50), axis=1).shape, (2, 3, 5, 6))
+        assert_equal(np.percentile(x, (25, 50), axis=2).shape, (2, 3, 4, 6))
+        assert_equal(np.percentile(x, (25, 50), axis=3).shape, (2, 3, 4, 5))
+        assert_equal(
+            np.percentile(x, (25, 50, 75), axis=1).shape, (3, 3, 5, 6))
+        assert_equal(np.percentile(x, (25, 50),
+                                   method="higher").shape, (2,))
+        assert_equal(np.percentile(x, (25, 50, 75),
+                                   method="higher").shape, (3,))
+        assert_equal(np.percentile(x, (25, 50), axis=0,
+                                   method="higher").shape, (2, 4, 5, 6))
+        assert_equal(np.percentile(x, (25, 50), axis=1,
+                                   method="higher").shape, (2, 3, 5, 6))
+        assert_equal(np.percentile(x, (25, 50), axis=2,
+                                   method="higher").shape, (2, 3, 4, 6))
+        assert_equal(np.percentile(x, (25, 50), axis=3,
+                                   method="higher").shape, (2, 3, 4, 5))
+        assert_equal(np.percentile(x, (25, 50, 75), axis=1,
+                                   method="higher").shape, (3, 3, 5, 6))
+
+    def test_scalar_q(self):
+        # test for no empty dimensions for compatibility with old percentile
+        x = np.arange(12).reshape(3, 4)
+        assert_equal(np.percentile(x, 50), 5.5)
+        assert_(np.isscalar(np.percentile(x, 50)))
+        r0 = np.array([4.,  5.,  6.,  7.])
+        assert_equal(np.percentile(x, 50, axis=0), r0)
+        assert_equal(np.percentile(x, 50, axis=0).shape, r0.shape)
+        r1 = np.array([1.5,  5.5,  9.5])
+        assert_almost_equal(np.percentile(x, 50, axis=1), r1)
+        assert_equal(np.percentile(x, 50, axis=1).shape, r1.shape)
+
+        out = np.empty(1)
+        assert_equal(np.percentile(x, 50, out=out), 5.5)
+        assert_equal(out, 5.5)
+        out = np.empty(4)
+        assert_equal(np.percentile(x, 50, axis=0, out=out), r0)
+        assert_equal(out, r0)
+        out = np.empty(3)
+        assert_equal(np.percentile(x, 50, axis=1, out=out), r1)
+        assert_equal(out, r1)
+
+        # test for no empty dimensions for compatibility with old percentile
+        x = np.arange(12).reshape(3, 4)
+        assert_equal(np.percentile(x, 50, method='lower'), 5.)
+        assert_(np.isscalar(np.percentile(x, 50)))
+        r0 = np.array([4.,  5.,  6.,  7.])
+        c0 = np.percentile(x, 50, method='lower', axis=0)
+        assert_equal(c0, r0)
+        assert_equal(c0.shape, r0.shape)
+        r1 = np.array([1.,  5.,  9.])
+        c1 = np.percentile(x, 50, method='lower', axis=1)
+        assert_almost_equal(c1, r1)
+        assert_equal(c1.shape, r1.shape)
+
+        out = np.empty((), dtype=x.dtype)
+        c = np.percentile(x, 50, method='lower', out=out)
+        assert_equal(c, 5)
+        assert_equal(out, 5)
+        out = np.empty(4, dtype=x.dtype)
+        c = np.percentile(x, 50, method='lower', axis=0, out=out)
+        assert_equal(c, r0)
+        assert_equal(out, r0)
+        out = np.empty(3, dtype=x.dtype)
+        c = np.percentile(x, 50, method='lower', axis=1, out=out)
+        assert_equal(c, r1)
+        assert_equal(out, r1)
+
+    def test_exception(self):
+        assert_raises(ValueError, np.percentile, [1, 2], 56,
+                      method='foobar')
+        assert_raises(ValueError, np.percentile, [1], 101)
+        assert_raises(ValueError, np.percentile, [1], -1)
+        assert_raises(ValueError, np.percentile, [1], list(range(50)) + [101])
+        assert_raises(ValueError, np.percentile, [1], list(range(50)) + [-0.1])
+
+    def test_percentile_list(self):
+        assert_equal(np.percentile([1, 2, 3], 0), 1)
+
+    def test_percentile_out(self):
+        x = np.array([1, 2, 3])
+        y = np.zeros((3,))
+        p = (1, 2, 3)
+        np.percentile(x, p, out=y)
+        assert_equal(np.percentile(x, p), y)
+
+        x = np.array([[1, 2, 3],
+                      [4, 5, 6]])
+
+        y = np.zeros((3, 3))
+        np.percentile(x, p, axis=0, out=y)
+        assert_equal(np.percentile(x, p, axis=0), y)
+
+        y = np.zeros((3, 2))
+        np.percentile(x, p, axis=1, out=y)
+        assert_equal(np.percentile(x, p, axis=1), y)
+
+        x = np.arange(12).reshape(3, 4)
+        # q.dim > 1, float
+        r0 = np.array([[2.,  3.,  4., 5.], [4., 5., 6., 7.]])
+        out = np.empty((2, 4))
+        assert_equal(np.percentile(x, (25, 50), axis=0, out=out), r0)
+        assert_equal(out, r0)
+        r1 = np.array([[0.75,  4.75,  8.75], [1.5,  5.5,  9.5]])
+        out = np.empty((2, 3))
+        assert_equal(np.percentile(x, (25, 50), axis=1, out=out), r1)
+        assert_equal(out, r1)
+
+        # q.dim > 1, int
+        r0 = np.array([[0,  1,  2, 3], [4, 5, 6, 7]])
+        out = np.empty((2, 4), dtype=x.dtype)
+        c = np.percentile(x, (25, 50), method='lower', axis=0, out=out)
+        assert_equal(c, r0)
+        assert_equal(out, r0)
+        r1 = np.array([[0,  4,  8], [1,  5,  9]])
+        out = np.empty((2, 3), dtype=x.dtype)
+        c = np.percentile(x, (25, 50), method='lower', axis=1, out=out)
+        assert_equal(c, r1)
+        assert_equal(out, r1)
+
+    def test_percentile_empty_dim(self):
+        # empty dims are preserved
+        d = np.arange(11 * 2).reshape(11, 1, 2, 1)
+        assert_array_equal(np.percentile(d, 50, axis=0).shape, (1, 2, 1))
+        assert_array_equal(np.percentile(d, 50, axis=1).shape, (11, 2, 1))
+        assert_array_equal(np.percentile(d, 50, axis=2).shape, (11, 1, 1))
+        assert_array_equal(np.percentile(d, 50, axis=3).shape, (11, 1, 2))
+        assert_array_equal(np.percentile(d, 50, axis=-1).shape, (11, 1, 2))
+        assert_array_equal(np.percentile(d, 50, axis=-2).shape, (11, 1, 1))
+        assert_array_equal(np.percentile(d, 50, axis=-3).shape, (11, 2, 1))
+        assert_array_equal(np.percentile(d, 50, axis=-4).shape, (1, 2, 1))
+
+        assert_array_equal(np.percentile(d, 50, axis=2,
+                                         method='midpoint').shape,
+                           (11, 1, 1))
+        assert_array_equal(np.percentile(d, 50, axis=-2,
+                                         method='midpoint').shape,
+                           (11, 1, 1))
+
+        assert_array_equal(np.array(np.percentile(d, [10, 50], axis=0)).shape,
+                           (2, 1, 2, 1))
+        assert_array_equal(np.array(np.percentile(d, [10, 50], axis=1)).shape,
+                           (2, 11, 2, 1))
+        assert_array_equal(np.array(np.percentile(d, [10, 50], axis=2)).shape,
+                           (2, 11, 1, 1))
+        assert_array_equal(np.array(np.percentile(d, [10, 50], axis=3)).shape,
+                           (2, 11, 1, 2))
+
+    def test_percentile_no_overwrite(self):
+        a = np.array([2, 3, 4, 1])
+        np.percentile(a, [50], overwrite_input=False)
+        assert_equal(a, np.array([2, 3, 4, 1]))
+
+        a = np.array([2, 3, 4, 1])
+        np.percentile(a, [50])
+        assert_equal(a, np.array([2, 3, 4, 1]))
+
+    def test_no_p_overwrite(self):
+        p = np.linspace(0., 100., num=5)
+        np.percentile(np.arange(100.), p, method="midpoint")
+        assert_array_equal(p, np.linspace(0., 100., num=5))
+        p = np.linspace(0., 100., num=5).tolist()
+        np.percentile(np.arange(100.), p, method="midpoint")
+        assert_array_equal(p, np.linspace(0., 100., num=5).tolist())
+
+    def test_percentile_overwrite(self):
+        a = np.array([2, 3, 4, 1])
+        b = np.percentile(a, [50], overwrite_input=True)
+        assert_equal(b, np.array([2.5]))
+
+        b = np.percentile([2, 3, 4, 1], [50], overwrite_input=True)
+        assert_equal(b, np.array([2.5]))
+
+    def test_extended_axis(self):
+        o = np.random.normal(size=(71, 23))
+        x = np.dstack([o] * 10)
+        assert_equal(np.percentile(x, 30, axis=(0, 1)), np.percentile(o, 30))
+        x = np.moveaxis(x, -1, 0)
+        assert_equal(np.percentile(x, 30, axis=(-2, -1)), np.percentile(o, 30))
+        x = x.swapaxes(0, 1).copy()
+        assert_equal(np.percentile(x, 30, axis=(0, -1)), np.percentile(o, 30))
+        x = x.swapaxes(0, 1).copy()
+
+        assert_equal(np.percentile(x, [25, 60], axis=(0, 1, 2)),
+                     np.percentile(x, [25, 60], axis=None))
+        assert_equal(np.percentile(x, [25, 60], axis=(0,)),
+                     np.percentile(x, [25, 60], axis=0))
+
+        d = np.arange(3 * 5 * 7 * 11).reshape((3, 5, 7, 11))
+        np.random.shuffle(d.ravel())
+        assert_equal(np.percentile(d, 25,  axis=(0, 1, 2))[0],
+                     np.percentile(d[:,:,:, 0].flatten(), 25))
+        assert_equal(np.percentile(d, [10, 90], axis=(0, 1, 3))[:, 1],
+                     np.percentile(d[:,:, 1,:].flatten(), [10, 90]))
+        assert_equal(np.percentile(d, 25, axis=(3, 1, -4))[2],
+                     np.percentile(d[:,:, 2,:].flatten(), 25))
+        assert_equal(np.percentile(d, 25, axis=(3, 1, 2))[2],
+                     np.percentile(d[2,:,:,:].flatten(), 25))
+        assert_equal(np.percentile(d, 25, axis=(3, 2))[2, 1],
+                     np.percentile(d[2, 1,:,:].flatten(), 25))
+        assert_equal(np.percentile(d, 25, axis=(1, -2))[2, 1],
+                     np.percentile(d[2,:,:, 1].flatten(), 25))
+        assert_equal(np.percentile(d, 25, axis=(1, 3))[2, 2],
+                     np.percentile(d[2,:, 2,:].flatten(), 25))
+
+    def test_extended_axis_invalid(self):
+        d = np.ones((3, 5, 7, 11))
+        assert_raises(np.AxisError, np.percentile, d, axis=-5, q=25)
+        assert_raises(np.AxisError, np.percentile, d, axis=(0, -5), q=25)
+        assert_raises(np.AxisError, np.percentile, d, axis=4, q=25)
+        assert_raises(np.AxisError, np.percentile, d, axis=(0, 4), q=25)
+        # each of these refers to the same axis twice
+        assert_raises(ValueError, np.percentile, d, axis=(1, 1), q=25)
+        assert_raises(ValueError, np.percentile, d, axis=(-1, -1), q=25)
+        assert_raises(ValueError, np.percentile, d, axis=(3, -1), q=25)
+
+    def test_keepdims(self):
+        d = np.ones((3, 5, 7, 11))
+        assert_equal(np.percentile(d, 7, axis=None, keepdims=True).shape,
+                     (1, 1, 1, 1))
+        assert_equal(np.percentile(d, 7, axis=(0, 1), keepdims=True).shape,
+                     (1, 1, 7, 11))
+        assert_equal(np.percentile(d, 7, axis=(0, 3), keepdims=True).shape,
+                     (1, 5, 7, 1))
+        assert_equal(np.percentile(d, 7, axis=(1,), keepdims=True).shape,
+                     (3, 1, 7, 11))
+        assert_equal(np.percentile(d, 7, (0, 1, 2, 3), keepdims=True).shape,
+                     (1, 1, 1, 1))
+        assert_equal(np.percentile(d, 7, axis=(0, 1, 3), keepdims=True).shape,
+                     (1, 1, 7, 1))
+
+        assert_equal(np.percentile(d, [1, 7], axis=(0, 1, 3),
+                                   keepdims=True).shape, (2, 1, 1, 7, 1))
+        assert_equal(np.percentile(d, [1, 7], axis=(0, 3),
+                                   keepdims=True).shape, (2, 1, 5, 7, 1))
+
+    @pytest.mark.parametrize('q', [7, [1, 7]])
+    @pytest.mark.parametrize(
+        argnames='axis',
+        argvalues=[
+            None,
+            1,
+            (1,),
+            (0, 1),
+            (-3, -1),
+        ]
+    )
+    def test_keepdims_out(self, q, axis):
+        d = np.ones((3, 5, 7, 11))
+        if axis is None:
+            shape_out = (1,) * d.ndim
+        else:
+            axis_norm = normalize_axis_tuple(axis, d.ndim)
+            shape_out = tuple(
+                1 if i in axis_norm else d.shape[i] for i in range(d.ndim))
+        shape_out = np.shape(q) + shape_out
+
+        out = np.empty(shape_out)
+        result = np.percentile(d, q, axis=axis, keepdims=True, out=out)
+        assert result is out
+        assert_equal(result.shape, shape_out)
+
+    def test_out(self):
+        o = np.zeros((4,))
+        d = np.ones((3, 4))
+        assert_equal(np.percentile(d, 0, 0, out=o), o)
+        assert_equal(np.percentile(d, 0, 0, method='nearest', out=o), o)
+        o = np.zeros((3,))
+        assert_equal(np.percentile(d, 1, 1, out=o), o)
+        assert_equal(np.percentile(d, 1, 1, method='nearest', out=o), o)
+
+        o = np.zeros(())
+        assert_equal(np.percentile(d, 2, out=o), o)
+        assert_equal(np.percentile(d, 2, method='nearest', out=o), o)
+
+    def test_out_nan(self):
+        with warnings.catch_warnings(record=True):
+            warnings.filterwarnings('always', '', RuntimeWarning)
+            o = np.zeros((4,))
+            d = np.ones((3, 4))
+            d[2, 1] = np.nan
+            assert_equal(np.percentile(d, 0, 0, out=o), o)
+            assert_equal(
+                np.percentile(d, 0, 0, method='nearest', out=o), o)
+            o = np.zeros((3,))
+            assert_equal(np.percentile(d, 1, 1, out=o), o)
+            assert_equal(
+                np.percentile(d, 1, 1, method='nearest', out=o), o)
+            o = np.zeros(())
+            assert_equal(np.percentile(d, 1, out=o), o)
+            assert_equal(
+                np.percentile(d, 1, method='nearest', out=o), o)
+
+    def test_nan_behavior(self):
+        a = np.arange(24, dtype=float)
+        a[2] = np.nan
+        assert_equal(np.percentile(a, 0.3), np.nan)
+        assert_equal(np.percentile(a, 0.3, axis=0), np.nan)
+        assert_equal(np.percentile(a, [0.3, 0.6], axis=0),
+                     np.array([np.nan] * 2))
+
+        a = np.arange(24, dtype=float).reshape(2, 3, 4)
+        a[1, 2, 3] = np.nan
+        a[1, 1, 2] = np.nan
+
+        # no axis
+        assert_equal(np.percentile(a, 0.3), np.nan)
+        assert_equal(np.percentile(a, 0.3).ndim, 0)
+
+        # axis0 zerod
+        b = np.percentile(np.arange(24, dtype=float).reshape(2, 3, 4), 0.3, 0)
+        b[2, 3] = np.nan
+        b[1, 2] = np.nan
+        assert_equal(np.percentile(a, 0.3, 0), b)
+
+        # axis0 not zerod
+        b = np.percentile(np.arange(24, dtype=float).reshape(2, 3, 4),
+                          [0.3, 0.6], 0)
+        b[:, 2, 3] = np.nan
+        b[:, 1, 2] = np.nan
+        assert_equal(np.percentile(a, [0.3, 0.6], 0), b)
+
+        # axis1 zerod
+        b = np.percentile(np.arange(24, dtype=float).reshape(2, 3, 4), 0.3, 1)
+        b[1, 3] = np.nan
+        b[1, 2] = np.nan
+        assert_equal(np.percentile(a, 0.3, 1), b)
+        # axis1 not zerod
+        b = np.percentile(
+            np.arange(24, dtype=float).reshape(2, 3, 4), [0.3, 0.6], 1)
+        b[:, 1, 3] = np.nan
+        b[:, 1, 2] = np.nan
+        assert_equal(np.percentile(a, [0.3, 0.6], 1), b)
+
+        # axis02 zerod
+        b = np.percentile(
+            np.arange(24, dtype=float).reshape(2, 3, 4), 0.3, (0, 2))
+        b[1] = np.nan
+        b[2] = np.nan
+        assert_equal(np.percentile(a, 0.3, (0, 2)), b)
+        # axis02 not zerod
+        b = np.percentile(np.arange(24, dtype=float).reshape(2, 3, 4),
+                          [0.3, 0.6], (0, 2))
+        b[:, 1] = np.nan
+        b[:, 2] = np.nan
+        assert_equal(np.percentile(a, [0.3, 0.6], (0, 2)), b)
+        # axis02 not zerod with method='nearest'
+        b = np.percentile(np.arange(24, dtype=float).reshape(2, 3, 4),
+                          [0.3, 0.6], (0, 2), method='nearest')
+        b[:, 1] = np.nan
+        b[:, 2] = np.nan
+        assert_equal(np.percentile(
+            a, [0.3, 0.6], (0, 2), method='nearest'), b)
+
+    def test_nan_q(self):
+        # GH18830
+        with pytest.raises(ValueError, match="Percentiles must be in"):
+            np.percentile([1, 2, 3, 4.0], np.nan)
+        with pytest.raises(ValueError, match="Percentiles must be in"):
+            np.percentile([1, 2, 3, 4.0], [np.nan])
+        q = np.linspace(1.0, 99.0, 16)
+        q[0] = np.nan
+        with pytest.raises(ValueError, match="Percentiles must be in"):
+            np.percentile([1, 2, 3, 4.0], q)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestQuantile:
+    # most of this is already tested by TestPercentile
+
+    def test_max_ulp(self):
+        x = [0.0, 0.2, 0.4]
+        a = np.quantile(x, 0.45)
+        # The default linear method would result in 0 + 0.2 * (0.45/2) = 0.18.
+        # 0.18 is not exactly representable and the formula leads to a 1 ULP
+        # different result. Ensure it is this exact within 1 ULP, see gh-20331.
+        np.testing.assert_array_max_ulp(a, 0.18, maxulp=1)
+
+    def test_basic(self):
+        x = np.arange(8) * 0.5
+        assert_equal(np.quantile(x, 0), 0.)
+        assert_equal(np.quantile(x, 1), 3.5)
+        assert_equal(np.quantile(x, 0.5), 1.75)
+
+    def test_correct_quantile_value(self):
+        a = np.array([True])
+        tf_quant = np.quantile(True, False)
+        assert_equal(tf_quant, a[0])
+        assert_equal(type(tf_quant), a.dtype)
+        a = np.array([False, True, True])
+        quant_res = np.quantile(a, a)
+        assert_array_equal(quant_res, a)
+        assert_equal(quant_res.dtype, a.dtype)
+
+    def test_fraction(self):
+        # fractional input, integral quantile
+        x = [Fraction(i, 2) for i in range(8)]
+        q = np.quantile(x, 0)
+        assert_equal(q, 0)
+        assert_equal(type(q), Fraction)
+
+        q = np.quantile(x, 1)
+        assert_equal(q, Fraction(7, 2))
+        assert_equal(type(q), Fraction)
+
+        q = np.quantile(x, Fraction(1, 2))
+        assert_equal(q, Fraction(7, 4))
+        assert_equal(type(q), Fraction)
+
+        q = np.quantile(x, [Fraction(1, 2)])
+        assert_equal(q, np.array([Fraction(7, 4)]))
+        assert_equal(type(q), np.ndarray)
+
+        q = np.quantile(x, [[Fraction(1, 2)]])
+        assert_equal(q, np.array([[Fraction(7, 4)]]))
+        assert_equal(type(q), np.ndarray)
+
+        # repeat with integral input but fractional quantile
+        x = np.arange(8)
+        assert_equal(np.quantile(x, Fraction(1, 2)), Fraction(7, 2))
+
+    def test_complex(self):
+        #See gh-22652
+        arr_c = np.array([0.5+3.0j, 2.1+0.5j, 1.6+2.3j], dtype='G')
+        assert_raises(TypeError, np.quantile, arr_c, 0.5)
+        arr_c = np.array([0.5+3.0j, 2.1+0.5j, 1.6+2.3j], dtype='D')
+        assert_raises(TypeError, np.quantile, arr_c, 0.5)
+        arr_c = np.array([0.5+3.0j, 2.1+0.5j, 1.6+2.3j], dtype='F')
+        assert_raises(TypeError, np.quantile, arr_c, 0.5)
+
+    def test_no_p_overwrite(self):
+        # this is worth retesting, because quantile does not make a copy
+        p0 = np.array([0, 0.75, 0.25, 0.5, 1.0])
+        p = p0.copy()
+        np.quantile(np.arange(100.), p, method="midpoint")
+        assert_array_equal(p, p0)
+
+        p0 = p0.tolist()
+        p = p.tolist()
+        np.quantile(np.arange(100.), p, method="midpoint")
+        assert_array_equal(p, p0)
+
+    @pytest.mark.parametrize("dtype", np.typecodes["AllInteger"])
+    def test_quantile_preserve_int_type(self, dtype):
+        res = np.quantile(np.array([1, 2], dtype=dtype), [0.5],
+                          method="nearest")
+        assert res.dtype == dtype
+
+    @pytest.mark.parametrize("method",
+             ['inverted_cdf', 'averaged_inverted_cdf', 'closest_observation',
+              'interpolated_inverted_cdf', 'hazen', 'weibull', 'linear',
+              'median_unbiased', 'normal_unbiased',
+              'nearest', 'lower', 'higher', 'midpoint'])
+    def test_quantile_monotonic(self, method):
+        # GH 14685
+        # test that the return value of quantile is monotonic if p0 is ordered
+        # Also tests that the boundary values are not mishandled.
+        p0 = np.linspace(0, 1, 101)
+        quantile = np.quantile(np.array([0, 1, 1, 2, 2, 3, 3, 4, 5, 5, 1, 1, 9, 9, 9,
+                                         8, 8, 7]) * 0.1, p0, method=method)
+        assert_equal(np.sort(quantile), quantile)
+
+        # Also test one where the number of data points is clearly divisible:
+        quantile = np.quantile([0., 1., 2., 3.], p0, method=method)
+        assert_equal(np.sort(quantile), quantile)
+
+    @pytest.mark.skip(reason='no hypothesis')
+    @hypothesis.given(
+            arr=arrays(dtype=np.float64,
+                       shape=st.integers(min_value=3, max_value=1000),
+                       elements=st.floats(allow_infinity=False, allow_nan=False,
+                                          min_value=-1e300, max_value=1e300)))
+    def test_quantile_monotonic_hypo(self, arr):
+        p0 = np.arange(0, 1, 0.01)
+        quantile = np.quantile(arr, p0)
+        assert_equal(np.sort(quantile), quantile)
+
+    def test_quantile_scalar_nan(self):
+        a = np.array([[10., 7., 4.], [3., 2., 1.]])
+        a[0][1] = np.nan
+        actual = np.quantile(a, 0.5)
+        assert np.isscalar(actual)
+        assert_equal(np.quantile(a, 0.5), np.nan)
+
+
+@pytest.mark.skip(reason='no hypothesis')
+class TestLerp:
+    @hypothesis.given(t0=st.floats(allow_nan=False, allow_infinity=False,
+                                   min_value=0, max_value=1),
+                      t1=st.floats(allow_nan=False, allow_infinity=False,
+                                   min_value=0, max_value=1),
+                      a = st.floats(allow_nan=False, allow_infinity=False,
+                                    min_value=-1e300, max_value=1e300),
+                      b = st.floats(allow_nan=False, allow_infinity=False,
+                                    min_value=-1e300, max_value=1e300))
+    def test_linear_interpolation_formula_monotonic(self, t0, t1, a, b):
+        l0 = nfb._lerp(a, b, t0)
+        l1 = nfb._lerp(a, b, t1)
+        if t0 == t1 or a == b:
+            assert l0 == l1  # uninteresting
+        elif (t0 < t1) == (a < b):
+            assert l0 <= l1
+        else:
+            assert l0 >= l1
+
+    @hypothesis.given(t=st.floats(allow_nan=False, allow_infinity=False,
+                                  min_value=0, max_value=1),
+                      a=st.floats(allow_nan=False, allow_infinity=False,
+                                  min_value=-1e300, max_value=1e300),
+                      b=st.floats(allow_nan=False, allow_infinity=False,
+                                  min_value=-1e300, max_value=1e300))
+    def test_linear_interpolation_formula_bounded(self, t, a, b):
+        if a <= b:
+            assert a <= nfb._lerp(a, b, t) <= b
+        else:
+            assert b <= nfb._lerp(a, b, t) <= a
+
+    @hypothesis.given(t=st.floats(allow_nan=False, allow_infinity=False,
+                                  min_value=0, max_value=1),
+                      a=st.floats(allow_nan=False, allow_infinity=False,
+                                  min_value=-1e300, max_value=1e300),
+                      b=st.floats(allow_nan=False, allow_infinity=False,
+                                  min_value=-1e300, max_value=1e300))
+    def test_linear_interpolation_formula_symmetric(self, t, a, b):
+        # double subtraction is needed to remove the extra precision of t < 0.5
+        left = nfb._lerp(a, b, 1 - (1 - t))
+        right = nfb._lerp(b, a, 1 - t)
+        assert_allclose(left, right)
+
+    def test_linear_interpolation_formula_0d_inputs(self):
+        a = np.array(2)
+        b = np.array(5)
+        t = np.array(0.2)
+        assert nfb._lerp(a, b, t) == 2.6
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestMedian:
+
+    def test_basic(self):
+        a0 = np.array(1)
+        a1 = np.arange(2)
+        a2 = np.arange(6).reshape(2, 3)
+        assert_equal(np.median(a0), 1)
+        assert_allclose(np.median(a1), 0.5)
+        assert_allclose(np.median(a2), 2.5)
+        assert_allclose(np.median(a2, axis=0), [1.5,  2.5,  3.5])
+        assert_equal(np.median(a2, axis=1), [1, 4])
+        assert_allclose(np.median(a2, axis=None), 2.5)
+
+        a = np.array([0.0444502, 0.0463301, 0.141249, 0.0606775])
+        assert_almost_equal((a[1] + a[3]) / 2., np.median(a))
+        a = np.array([0.0463301, 0.0444502, 0.141249])
+        assert_equal(a[0], np.median(a))
+        a = np.array([0.0444502, 0.141249, 0.0463301])
+        assert_equal(a[-1], np.median(a))
+        # check array scalar result
+        assert_equal(np.median(a).ndim, 0)
+        a[1] = np.nan
+        assert_equal(np.median(a).ndim, 0)
+
+    def test_axis_keyword(self):
+        a3 = np.array([[2, 3],
+                       [0, 1],
+                       [6, 7],
+                       [4, 5]])
+        for a in [a3, np.random.randint(0, 100, size=(2, 3, 4))]:
+            orig = a.copy()
+            np.median(a, axis=None)
+            for ax in range(a.ndim):
+                np.median(a, axis=ax)
+            assert_array_equal(a, orig)
+
+        assert_allclose(np.median(a3, axis=0), [3,  4])
+        assert_allclose(np.median(a3.T, axis=1), [3,  4])
+        assert_allclose(np.median(a3), 3.5)
+        assert_allclose(np.median(a3, axis=None), 3.5)
+        assert_allclose(np.median(a3.T), 3.5)
+
+    def test_overwrite_keyword(self):
+        a3 = np.array([[2, 3],
+                       [0, 1],
+                       [6, 7],
+                       [4, 5]])
+        a0 = np.array(1)
+        a1 = np.arange(2)
+        a2 = np.arange(6).reshape(2, 3)
+        assert_allclose(np.median(a0.copy(), overwrite_input=True), 1)
+        assert_allclose(np.median(a1.copy(), overwrite_input=True), 0.5)
+        assert_allclose(np.median(a2.copy(), overwrite_input=True), 2.5)
+        assert_allclose(np.median(a2.copy(), overwrite_input=True, axis=0),
+                        [1.5,  2.5,  3.5])
+        assert_allclose(
+            np.median(a2.copy(), overwrite_input=True, axis=1), [1, 4])
+        assert_allclose(
+            np.median(a2.copy(), overwrite_input=True, axis=None), 2.5)
+        assert_allclose(
+            np.median(a3.copy(), overwrite_input=True, axis=0), [3,  4])
+        assert_allclose(np.median(a3.T.copy(), overwrite_input=True, axis=1),
+                        [3,  4])
+
+        a4 = np.arange(3 * 4 * 5, dtype=np.float32).reshape((3, 4, 5))
+        np.random.shuffle(a4.ravel())
+        assert_allclose(np.median(a4, axis=None),
+                        np.median(a4.copy(), axis=None, overwrite_input=True))
+        assert_allclose(np.median(a4, axis=0),
+                        np.median(a4.copy(), axis=0, overwrite_input=True))
+        assert_allclose(np.median(a4, axis=1),
+                        np.median(a4.copy(), axis=1, overwrite_input=True))
+        assert_allclose(np.median(a4, axis=2),
+                        np.median(a4.copy(), axis=2, overwrite_input=True))
+
+    def test_array_like(self):
+        x = [1, 2, 3]
+        assert_almost_equal(np.median(x), 2)
+        x2 = [x]
+        assert_almost_equal(np.median(x2), 2)
+        assert_allclose(np.median(x2, axis=0), x)
+
+    def test_subclass(self):
+        # gh-3846
+        class MySubClass(np.ndarray):
+
+            def __new__(cls, input_array, info=None):
+                obj = np.asarray(input_array).view(cls)
+                obj.info = info
+                return obj
+
+            def mean(self, axis=None, dtype=None, out=None):
+                return -7
+
+        a = MySubClass([1, 2, 3])
+        assert_equal(np.median(a), -7)
+
+    @pytest.mark.parametrize('arr',
+                             ([1., 2., 3.], [1., np.nan, 3.], np.nan, 0.))
+    def test_subclass2(self, arr):
+        """Check that we return subclasses, even if a NaN scalar."""
+        class MySubclass(np.ndarray):
+            pass
+
+        m = np.median(np.array(arr).view(MySubclass))
+        assert isinstance(m, MySubclass)
+
+    def test_out(self):
+        o = np.zeros((4,))
+        d = np.ones((3, 4))
+        assert_equal(np.median(d, 0, out=o), o)
+        o = np.zeros((3,))
+        assert_equal(np.median(d, 1, out=o), o)
+        o = np.zeros(())
+        assert_equal(np.median(d, out=o), o)
+
+    def test_out_nan(self):
+        with warnings.catch_warnings(record=True):
+            warnings.filterwarnings('always', '', RuntimeWarning)
+            o = np.zeros((4,))
+            d = np.ones((3, 4))
+            d[2, 1] = np.nan
+            assert_equal(np.median(d, 0, out=o), o)
+            o = np.zeros((3,))
+            assert_equal(np.median(d, 1, out=o), o)
+            o = np.zeros(())
+            assert_equal(np.median(d, out=o), o)
+
+    def test_nan_behavior(self):
+        a = np.arange(24, dtype=float)
+        a[2] = np.nan
+        assert_equal(np.median(a), np.nan)
+        assert_equal(np.median(a, axis=0), np.nan)
+
+        a = np.arange(24, dtype=float).reshape(2, 3, 4)
+        a[1, 2, 3] = np.nan
+        a[1, 1, 2] = np.nan
+
+        # no axis
+        assert_equal(np.median(a), np.nan)
+        assert_equal(np.median(a).ndim, 0)
+
+        # axis0
+        b = np.median(np.arange(24, dtype=float).reshape(2, 3, 4), 0)
+        b[2, 3] = np.nan
+        b[1, 2] = np.nan
+        assert_equal(np.median(a, 0), b)
+
+        # axis1
+        b = np.median(np.arange(24, dtype=float).reshape(2, 3, 4), 1)
+        b[1, 3] = np.nan
+        b[1, 2] = np.nan
+        assert_equal(np.median(a, 1), b)
+
+        # axis02
+        b = np.median(np.arange(24, dtype=float).reshape(2, 3, 4), (0, 2))
+        b[1] = np.nan
+        b[2] = np.nan
+        assert_equal(np.median(a, (0, 2)), b)
+
+    @pytest.mark.skipif(IS_WASM, reason="fp errors don't work correctly")
+    def test_empty(self):
+        # mean(empty array) emits two warnings: empty slice and divide by 0
+        a = np.array([], dtype=float)
+        with warnings.catch_warnings(record=True) as w:
+            warnings.filterwarnings('always', '', RuntimeWarning)
+            assert_equal(np.median(a), np.nan)
+            assert_(w[0].category is RuntimeWarning)
+            assert_equal(len(w), 2)
+
+        # multiple dimensions
+        a = np.array([], dtype=float, ndmin=3)
+        # no axis
+        with warnings.catch_warnings(record=True) as w:
+            warnings.filterwarnings('always', '', RuntimeWarning)
+            assert_equal(np.median(a), np.nan)
+            assert_(w[0].category is RuntimeWarning)
+
+        # axis 0 and 1
+        b = np.array([], dtype=float, ndmin=2)
+        assert_equal(np.median(a, axis=0), b)
+        assert_equal(np.median(a, axis=1), b)
+
+        # axis 2
+        b = np.array(np.nan, dtype=float, ndmin=2)
+        with warnings.catch_warnings(record=True) as w:
+            warnings.filterwarnings('always', '', RuntimeWarning)
+            assert_equal(np.median(a, axis=2), b)
+            assert_(w[0].category is RuntimeWarning)
+
+    def test_object(self):
+        o = np.arange(7.)
+        assert_(type(np.median(o.astype(object))), float)
+        o[2] = np.nan
+        assert_(type(np.median(o.astype(object))), float)
+
+    def test_extended_axis(self):
+        o = np.random.normal(size=(71, 23))
+        x = np.dstack([o] * 10)
+        assert_equal(np.median(x, axis=(0, 1)), np.median(o))
+        x = np.moveaxis(x, -1, 0)
+        assert_equal(np.median(x, axis=(-2, -1)), np.median(o))
+        x = x.swapaxes(0, 1).copy()
+        assert_equal(np.median(x, axis=(0, -1)), np.median(o))
+
+        assert_equal(np.median(x, axis=(0, 1, 2)), np.median(x, axis=None))
+        assert_equal(np.median(x, axis=(0, )), np.median(x, axis=0))
+        assert_equal(np.median(x, axis=(-1, )), np.median(x, axis=-1))
+
+        d = np.arange(3 * 5 * 7 * 11).reshape((3, 5, 7, 11))
+        np.random.shuffle(d.ravel())
+        assert_equal(np.median(d, axis=(0, 1, 2))[0],
+                     np.median(d[:,:,:, 0].flatten()))
+        assert_equal(np.median(d, axis=(0, 1, 3))[1],
+                     np.median(d[:,:, 1,:].flatten()))
+        assert_equal(np.median(d, axis=(3, 1, -4))[2],
+                     np.median(d[:,:, 2,:].flatten()))
+        assert_equal(np.median(d, axis=(3, 1, 2))[2],
+                     np.median(d[2,:,:,:].flatten()))
+        assert_equal(np.median(d, axis=(3, 2))[2, 1],
+                     np.median(d[2, 1,:,:].flatten()))
+        assert_equal(np.median(d, axis=(1, -2))[2, 1],
+                     np.median(d[2,:,:, 1].flatten()))
+        assert_equal(np.median(d, axis=(1, 3))[2, 2],
+                     np.median(d[2,:, 2,:].flatten()))
+
+    def test_extended_axis_invalid(self):
+        d = np.ones((3, 5, 7, 11))
+        assert_raises(np.AxisError, np.median, d, axis=-5)
+        assert_raises(np.AxisError, np.median, d, axis=(0, -5))
+        assert_raises(np.AxisError, np.median, d, axis=4)
+        assert_raises(np.AxisError, np.median, d, axis=(0, 4))
+        assert_raises(ValueError, np.median, d, axis=(1, 1))
+
+    def test_keepdims(self):
+        d = np.ones((3, 5, 7, 11))
+        assert_equal(np.median(d, axis=None, keepdims=True).shape,
+                     (1, 1, 1, 1))
+        assert_equal(np.median(d, axis=(0, 1), keepdims=True).shape,
+                     (1, 1, 7, 11))
+        assert_equal(np.median(d, axis=(0, 3), keepdims=True).shape,
+                     (1, 5, 7, 1))
+        assert_equal(np.median(d, axis=(1,), keepdims=True).shape,
+                     (3, 1, 7, 11))
+        assert_equal(np.median(d, axis=(0, 1, 2, 3), keepdims=True).shape,
+                     (1, 1, 1, 1))
+        assert_equal(np.median(d, axis=(0, 1, 3), keepdims=True).shape,
+                     (1, 1, 7, 1))
+
+    @pytest.mark.parametrize(
+        argnames='axis',
+        argvalues=[
+            None,
+            1,
+            (1, ),
+            (0, 1),
+            (-3, -1),
+        ]
+    )
+    def test_keepdims_out(self, axis):
+        d = np.ones((3, 5, 7, 11))
+        if axis is None:
+            shape_out = (1,) * d.ndim
+        else:
+            axis_norm = normalize_axis_tuple(axis, d.ndim)
+            shape_out = tuple(
+                1 if i in axis_norm else d.shape[i] for i in range(d.ndim))
+        out = np.empty(shape_out)
+        result = np.median(d, axis=axis, keepdims=True, out=out)
+        assert result is out
+        assert_equal(result.shape, shape_out)
+
+
+@pytest.mark.xfail(reason='TODO: implement')
+class TestSortComplex:
+
+    @pytest.mark.parametrize("type_in, type_out", [
+        ('l', 'D'),
+        ('h', 'F'),
+        ('H', 'F'),
+        ('b', 'F'),
+        ('B', 'F'),
+        ('g', 'G'),
+        ])
+    def test_sort_real(self, type_in, type_out):
+        # sort_complex() type casting for real input types
+        a = np.array([5, 3, 6, 2, 1], dtype=type_in)
+        actual = np.sort_complex(a)
+        expected = np.sort(a).astype(type_out)
+        assert_equal(actual, expected)
+        assert_equal(actual.dtype, expected.dtype)
+
+    def test_sort_complex(self):
+        # sort_complex() handling of complex input
+        a = np.array([2 + 3j, 1 - 2j, 1 - 3j, 2 + 1j], dtype='D')
+        expected = np.array([1 - 3j, 1 - 2j, 2 + 1j, 2 + 3j], dtype='D')
+        actual = np.sort_complex(a)
+        assert_equal(actual, expected)
+        assert_equal(actual.dtype, expected.dtype)