TST: fix 9 xfails (pandas-dev#28776)

Author: jbrockmendel

pandas/core/dtypes/cast.py

@@ -375,7 +375,9 @@ def maybe_promote(dtype, fill_value=np.nan):
         if issubclass(dtype.type, np.bool_):
             dtype = np.object_
         elif issubclass(dtype.type, np.integer):
-            dtype = np.float64
+            dtype = np.dtype(np.float64)
+            if not isna(fill_value):
+                fill_value = dtype.type(fill_value)
     elif is_bool(fill_value):
         if not issubclass(dtype.type, np.bool_):
             dtype = np.object_

pandas/tests/dtypes/cast/test_promote.py

@@ -174,9 +174,6 @@ def test_maybe_promote_int_with_float(any_int_dtype, float_dtype, box):
     fill_dtype = np.dtype(float_dtype)
     boxed, box_dtype = box  # read from parametrized fixture
 
-    if float_dtype == "float32" and not boxed:
-        pytest.xfail("falsely upcasts to float64")
-
     # create array of given dtype; casts "1" to correct dtype
     fill_value = np.array([1], dtype=fill_dtype)[0]