DEPR: don't make Index instantiate Int64/Uint64/Flaot64Index

Author: Terji Petersen

pandas/tests/indexes/multi/test_setops.py

@@ -10,6 +10,10 @@
     Series,
 )
 import pandas._testing as tm
+from pandas.api.types import (
+    is_float_dtype,
+    is_unsigned_integer_dtype,
+)
 
 
 @pytest.mark.parametrize("case", [0.5, "xxx"])
@@ -624,14 +628,24 @@ def test_union_duplicates(index, request):
     expected = mi2.sort_values()
     tm.assert_index_equal(result, expected)
 
-    if mi2.levels[0].dtype == np.uint64 and (mi2.get_level_values(0) < 2**63).all():
+    if (
+        is_unsigned_integer_dtype(mi2.levels[0])
+        and (mi2.get_level_values(0) < 2**63).all()
+    ):
         # GH#47294 - union uses lib.fast_zip, converting data to Python integers
         # and loses type information. Result is then unsigned only when values are
         # sufficiently large to require unsigned dtype. This happens only if other
         # has dups or one of both have missing values
         expected = expected.set_levels(
             [expected.levels[0].astype(int), expected.levels[1]]
         )
+    elif is_float_dtype(mi2.levels[0]):
+        # mi2 has duplicates witch is a different path than above, Fix that path
+        # to use correct float dtype?
+        expected = expected.set_levels(
+            [expected.levels[0].astype(float), expected.levels[1]]
+        )
+
     result = mi1.union(mi2)
     tm.assert_index_equal(result, expected)