TST: Test aggregate with list values pandas-dev#25581

Author: KingOfTheShow69

pandas/tests/groupby/aggregate/test_aggregate.py

@@ -1413,3 +1413,13 @@ def test_multi_axis_1_raises(func):
     gb = df.groupby("a", axis=1)
     with pytest.raises(NotImplementedError, match="axis other than 0 is not supported"):
         gb.agg(func)
+
+def test_agg_of_list():
+    # GH#25581
+    df1 = pd.DataFrame([[20, 'A'], [20, 'B'], [30, 'C']])
+    result = df1.groupby(0).agg(pd.Series.mode)
+
+    expected = pd.DataFrame({0: [20, 30], 1: [['A', 'B'], 'C']})
+    expected = expected.set_index(0)
+
+    tm.assert_frame_equal(result, expected)