TST: Add list of tuples pd.factorize test (#18649)

Author: Licht-T

pandas/tests/test_algos.py

@@ -17,6 +17,7 @@
 from pandas._libs.hashtable import unique_label_indices
 from pandas.compat import lrange, range
 import pandas.core.algorithms as algos
+from pandas.core.common import _asarray_tuplesafe
 import pandas.util.testing as tm
 from pandas.compat.numpy import np_array_datetime64_compat
 from pandas.util.testing import assert_almost_equal
@@ -190,6 +191,33 @@ def test_factorize_nan(self):
         assert len(set(key)) == len(set(expected))
         tm.assert_numpy_array_equal(pd.isna(key), expected == na_sentinel)
 
+    @pytest.mark.parametrize("data,expected_label,expected_level", [
+        (
+            [(1, 1), (1, 2), (0, 0), (1, 2), 'nonsense'],
+            [0, 1, 2, 1, 3],
+            [(1, 1), (1, 2), (0, 0), 'nonsense']
+        ),
+        (
+            [(1, 1), (1, 2), (0, 0), (1, 2), (1, 2, 3)],
+            [0, 1, 2, 1, 3],
+            [(1, 1), (1, 2), (0, 0), (1, 2, 3)]
+        ),
+        (
+            [(1, 1), (1, 2), (0, 0), (1, 2)],
+            [0, 1, 2, 1],
+            [(1, 1), (1, 2), (0, 0)]
+        )
+    ])
+    def test_factorize_tuple_list(self, data, expected_label, expected_level):
+        # GH9454
+        result = pd.factorize(data)
+
+        tm.assert_numpy_array_equal(result[0],
+                                    np.array(expected_label, dtype=np.intp))
+
+        expected_level_array = _asarray_tuplesafe(expected_level, dtype=object)
+        tm.assert_numpy_array_equal(result[1], expected_level_array)
+
     def test_complex_sorting(self):
         # gh 12666 - check no segfault
         # Test not valid numpy versions older than 1.11