Removed MultiIndex union overloading

Author: realzachbrownjohn

pandas-stubs/core/indexes/multi.pyi

@@ -163,15 +163,8 @@ class MultiIndex(Index):
     def insert(self, loc, item): ...
     def delete(self, loc): ...
     def isin(self, values, level=...) -> np_1darray[np.bool]: ...
-    @overload
     def union(
         self,
-        other: Self | list[tuple[Hashable, ...]],
+        other: Self | Index | list[HashableT],
         sort: bool | None = ...,
     ) -> Self: ...
-    @overload
-    def union(
-        self,
-        other: Index | list[HashableT],
-        sort: bool | None = ...,
-    ) -> Index: ...

pandas-stubs/py.typed

@@ -1603,20 +1603,15 @@ def test_to_series() -> None:
     check(assert_type(Index(["1"]).to_series(), "pd.Series[str]"), pd.Series, str)
 
 
-def test_swaplevel_rettype() -> None:
-    """Test that swaplevel returns Self"""
+def test_multiindex_swaplevel_rettype() -> None:
+    """Test that union returns MultiIndex on MultiIndex input and swaplevel returns Self"""
     mi = pd.MultiIndex.from_product([["a", "b"], [1, 2]], names=["let", "num"])
+    mi2 = pd.MultiIndex.from_product([["a", "b"], [3, 4]], names=["let", "num"])
+
     check(
         assert_type(mi.swaplevel(0, 1), "pd.MultiIndex"),
         pd.MultiIndex,
     )
-
-
-def test_multiindex_union() -> None:
-    """Test that union returns MultiIndex on MultiIndex input"""
-    mi = pd.MultiIndex.from_product([["a", "b"], [1, 2]], names=["let", "num"])
-    mi2 = pd.MultiIndex.from_product([["a", "b"], [3, 4]], names=["let", "num"])
-
     check(
         assert_type(mi.union(mi2), "pd.MultiIndex"),
         pd.MultiIndex,