TST: Add tests for fixed issues

pandas/tests/frame/methods/test_sort_values.py

@@ -497,3 +497,22 @@ def test_sort_values_ignore_index(
 
         tm.assert_frame_equal(result_df, expected)
         tm.assert_frame_equal(df, DataFrame(original_dict))
+
+    def test_sort_values_nat_na_position_default(self):
+        # GH 13230
+        expected = pd.DataFrame(
+            {
+                "A": [1, 2, 3, 4, 4],
+                "date": pd.DatetimeIndex(
+                    [
+                        "2010-01-01 09:00:00",
+                        "2010-01-01 09:00:01",
+                        "2010-01-01 09:00:02",
+                        "2010-01-01 09:00:03",
+                        "NaT",
+                    ]
+                ),
+            }
+        )
+        result = expected.sort_values(["A", "date"])
+        tm.assert_frame_equal(result, expected)

pandas/tests/frame/test_apply.py

@@ -691,6 +691,18 @@ def test_apply_dup_names_multi_agg(self):
 
         tm.assert_frame_equal(result, expected)
 
+    def test_apply_nested_result_axis_1(self):
+        # GH 13820
+        def apply_list(row):
+            return [2 * row["A"], 2 * row["C"], 2 * row["B"]]
+
+        df = pd.DataFrame(np.zeros((4, 4)), columns=list("ABCD"))
+        result = df.apply(apply_list, axis=1)
+        expected = Series(
+            [[0.0, 0.0, 0.0], [0.0, 0.0, 0.0], [0.0, 0.0, 0.0], [0.0, 0.0, 0.0]]
+        )
+        tm.assert_series_equal(result, expected)
+
 
 class TestInferOutputShape:
     # the user has supplied an opaque UDF where

pandas/tests/frame/test_arithmetic.py

@@ -726,3 +726,14 @@ def test_zero_len_frame_with_series_corner_cases():
     result = df + ser
     expected = df
     tm.assert_frame_equal(result, expected)
+
+
+def test_frame_single_columns_object_sum_axis_1():
+    # GH 13758
+    data = {
+        "One": pd.Series(["A", 1.2, np.nan]),
+    }
+    df = pd.DataFrame(data)
+    result = df.sum(axis=1)
+    expected = pd.Series(["A", 1.2, 0])
+    tm.assert_series_equal(result, expected)

pandas/tests/series/test_apply.py

@@ -780,3 +780,10 @@ def test_apply_scaler_on_date_time_index_aware_series(self):
         series = tm.makeTimeSeries(nper=30).tz_localize("UTC")
         result = pd.Series(series.index).apply(lambda x: 1)
         tm.assert_series_equal(result, pd.Series(np.ones(30), dtype="int64"))
+
+    def test_map_float_to_string_precision(self):
+        # GH 13228
+        ser = pd.Series(1 / 3)
+        result = ser.map(lambda val: str(val)).to_dict()
+        expected = {0: "0.3333333333333333"}
+        assert result == expected

pandas/tests/series/test_arithmetic.py

@@ -47,6 +47,22 @@ def test_flex_method_equivalence(self, opname, ts):
             expected = alt(other, series)
             tm.assert_almost_equal(result, expected)
 
+    def test_flex_method_subclass_metadata_preservation(self, all_arithmetic_operators):
+        # GH 13208
+        class MySeries(Series):
+            _metadata = ["x"]
+
+            @property
+            def _constructor(self):
+                return MySeries
+
+        opname = all_arithmetic_operators
+        op = getattr(Series, opname)
+        m = MySeries([1, 2, 3], name="test")
+        m.x = 42
+        result = op(m, 1)
+        assert result.x == 42
+
 
 class TestSeriesArithmetic:
     # Some of these may end up in tests/arithmetic, but are not yet sorted