TST: Add test for groupby.apply() to ensure metadata preservation in subclassed DataFrames and Series

Author: vgnshiyer

pandas/tests/groupby/test_groupby_subclass.py

@@ -97,7 +97,12 @@ def func2(group):
     result = custom_series.groupby(custom_df["c"]).agg(func2)
     tm.assert_series_equal(result, expected)
 
+
+def test_groupby_apply_preserves_metadata():
     # GH#62134 - Test that apply() preserves metadata when returning DataFrames/Series
+    custom_df = tm.SubclassedDataFrame({"a": [1, 2, 3], "b": [1, 1, 2], "c": [7, 8, 9]})
+    custom_df.testattr = "hello"
+
     def sum_func(group):
         assert isinstance(group, tm.SubclassedDataFrame)
         assert hasattr(group, "testattr")
@@ -108,6 +113,9 @@ def sum_func(group):
     assert hasattr(result, "testattr"), "DataFrame apply() should preserve metadata"
     assert result.testattr == "hello"
 
+    custom_series = tm.SubclassedSeries([1, 2, 3])
+    custom_series.testattr = "hello"
+
     def sum_series_func(group):
         assert isinstance(group, tm.SubclassedSeries)
         assert hasattr(group, "testattr")