Automatic level detection for dataframe reindex moved to generic.py and remove non-relevant test

Author: Roline Stapny Saldanha

pandas/core/frame.py

@@ -5355,18 +5355,6 @@ def reindex(
         limit: int | None = None,
         tolerance=None,
     ) -> DataFrame:
-        # Automatically detect matching level when reindexing from Index to MultiIndex.
-        # This prevents values from being incorrectly set to NaN when the source index
-        # name matches a level name in the target MultiIndex. Only applies when source
-        # is not already a MultiIndex.
-        if (
-            level is None
-            and index is not None
-            and isinstance(index, MultiIndex)
-            and not isinstance(self.index, MultiIndex)
-            and self.index.name in index.names
-        ):
-            level = self.index.name
         return super().reindex(
             labels=labels,
             index=index,

pandas/tests/series/methods/test_reindex.py

@@ -458,14 +458,3 @@ def test_reindex_multiindex_automatic_level(name, expected_match_level_a):
         expected = Series(np.nan, index=target, dtype=series.dtype)
 
     tm.assert_series_equal(result, expected)
-
-
-def test_reindex_multiindex_explicit_level_overrides():
-    series = Series([26.73, 24.255], index=Index([81, 82], name="a"))
-    target = MultiIndex.from_product(
-        [[81, 82], [np.nan], ["2018-06-01", "2018-07-01"]], names=["a", "b", "c"]
-    )
-
-    result = series.reindex(target, level=0)
-    expected = series.reindex(target, level="a")
-    tm.assert_series_equal(result, expected)