addresses comments (move _format_native_types, assert_index_equal etc.)

pandas/core/indexes/category.py

@@ -288,6 +288,9 @@ def astype(self, dtype, copy: bool = True) -> Index:
         dtype = pandas_dtype(dtype)
 
         cat = self.categories
+        # the super method always returns Int64Index, UInt64Index and Float64Index
+        # but if e.g. the categories are a NumIndex with dtype float32, we want to
+        # return an index with the same dtype as self.categories.
         if cat._is_num_index():
             assert isinstance(cat, NumIndex)  # mypy complaint fix
             try:

pandas/core/indexes/numeric.py

@@ -285,6 +285,32 @@ def _is_all_dates(self) -> bool:
         """
         return False
 
+    # ----------------------------------------------------------------
+
+    def _format_native_types(
+        self, na_rep="", float_format=None, decimal=".", quoting=None, **kwargs
+    ):
+        from pandas.io.formats.format import FloatArrayFormatter
+
+        if not is_float_dtype(self.dtype):
+            return super()._format_native_types(
+                na_rep=na_rep,
+                float_format=float_format,
+                decimal=decimal,
+                quoting=quoting,
+                **kwargs,
+            )
+
+        formatter = FloatArrayFormatter(
+            self._values,
+            na_rep=na_rep,
+            float_format=float_format,
+            decimal=decimal,
+            quoting=quoting,
+            fixed_width=False,
+        )
+        return formatter.get_result_as_array()
+
 
 class IntegerIndex(NumericIndex):
     """

pandas/tests/base/test_unique.py

@@ -24,9 +24,9 @@ def test_unique(index_or_series_obj):
         expected = pd.MultiIndex.from_tuples(unique_values)
         expected.names = obj.names
         tm.assert_index_equal(result, expected, exact=True)
-    elif isinstance(obj, pd.NumIndex):
+    elif type(obj) is pd.NumIndex:
         expected = pd.NumIndex(unique_values, dtype=obj.dtype)
-        tm.assert_index_equal(result, expected)
+        tm.assert_index_equal(result, expected, exact=True)
     elif isinstance(obj, pd.Index):
         expected = pd.Index(unique_values, dtype=obj.dtype)
         if is_datetime64tz_dtype(obj.dtype):
@@ -67,7 +67,7 @@ def test_unique_null(null_obj, index_or_series_obj):
 
     if type(obj) is pd.NumIndex:
         expected = pd.NumIndex(unique_values, dtype=obj.dtype)
-        tm.assert_index_equal(result, expected)
+        tm.assert_index_equal(result, expected, exact=True)
     elif isinstance(obj, pd.Index):
         expected = pd.Index(unique_values, dtype=obj.dtype)
         if is_datetime64tz_dtype(obj.dtype):

pandas/tests/indexes/test_setops.py

@@ -46,6 +46,7 @@
     (np.float32, np.uint32),
     (np.float32, np.uint16),
     (np.float32, np.uint8),
+    (np.float32, np.float64),
 ]