TST: reintroduce check_series_type in assert_series_equal (#32670)

Co-authored-by: Joris Van den Bossche <[email protected]>

Author: martinfleis

doc/source/whatsnew/v1.1.0.rst

@@ -396,6 +396,7 @@ Other
 - Set operations on an object-dtype :class:`Index` now always return object-dtype results (:issue:`31401`)
 - Bug in :meth:`AbstractHolidayCalendar.holidays` when no rules were defined (:issue:`31415`)
 - Bug in :meth:`DataFrame.to_records` incorrectly losing timezone information in timezone-aware ``datetime64`` columns (:issue:`32535`)
+- Fixed :func:`pandas.testing.assert_series_equal` to correctly raise if left object is a different subclass with ``check_series_type=True`` (:issue:`32670`).
 - :meth:`IntegerArray.astype` now supports ``datetime64`` dtype (:issue:32538`)
 
 .. ---------------------------------------------------------------------------

pandas/_testing.py

@@ -1050,6 +1050,7 @@ def assert_series_equal(
     right,
     check_dtype=True,
     check_index_type="equiv",
+    check_series_type=True,
     check_less_precise=False,
     check_names=True,
     check_exact=False,
@@ -1070,6 +1071,8 @@ def assert_series_equal(
     check_index_type : bool or {'equiv'}, default 'equiv'
         Whether to check the Index class, dtype and inferred_type
         are identical.
+    check_series_type : bool, default True
+         Whether to check the Series class is identical.
     check_less_precise : bool or int, default False
         Specify comparison precision. Only used when check_exact is False.
         5 digits (False) or 3 digits (True) after decimal points are compared.
@@ -1101,10 +1104,8 @@ def assert_series_equal(
     # instance validation
     _check_isinstance(left, right, Series)
 
-    # TODO: There are some tests using rhs is sparse
-    # lhs is dense. Should use assert_class_equal in future
-    assert isinstance(left, type(right))
-    # assert_class_equal(left, right, obj=obj)
+    if check_series_type:
+        assert_class_equal(left, right, obj=obj)
 
     # length comparison
     if len(left) != len(right):

pandas/tests/frame/test_subclass.py

@@ -163,12 +163,14 @@ def test_subclass_align_combinations(self):
 
         # frame + series
         res1, res2 = df.align(s, axis=0)
-        exp1 = pd.DataFrame(
+        exp1 = tm.SubclassedDataFrame(
             {"a": [1, np.nan, 3, np.nan, 5], "b": [1, np.nan, 3, np.nan, 5]},
             index=list("ABCDE"),
         )
         # name is lost when
-        exp2 = pd.Series([1, 2, np.nan, 4, np.nan], index=list("ABCDE"), name="x")
+        exp2 = tm.SubclassedSeries(
+            [1, 2, np.nan, 4, np.nan], index=list("ABCDE"), name="x"
+        )
 
         assert isinstance(res1, tm.SubclassedDataFrame)
         tm.assert_frame_equal(res1, exp1)

pandas/tests/util/test_assert_series_equal.py

@@ -194,3 +194,24 @@ def test_series_equal_categorical_mismatch(check_categorical):
             tm.assert_series_equal(s1, s2, check_categorical=check_categorical)
     else:
         _assert_series_equal_both(s1, s2, check_categorical=check_categorical)
+
+
+def test_series_equal_series_type():
+    class MySeries(Series):
+        pass
+
+    s1 = Series([1, 2])
+    s2 = Series([1, 2])
+    s3 = MySeries([1, 2])
+
+    tm.assert_series_equal(s1, s2, check_series_type=False)
+    tm.assert_series_equal(s1, s2, check_series_type=True)
+
+    tm.assert_series_equal(s1, s3, check_series_type=False)
+    tm.assert_series_equal(s3, s1, check_series_type=False)
+
+    with pytest.raises(AssertionError, match="Series classes are different"):
+        tm.assert_series_equal(s1, s3, check_series_type=True)
+
+    with pytest.raises(AssertionError, match="Series classes are different"):
+        tm.assert_series_equal(s3, s1, check_series_type=True)