TST: Fix maybe_promote xfails (#28754)

Author: jbrockmendel

pandas/core/dtypes/cast.py

@@ -348,12 +348,22 @@ def maybe_promote(dtype, fill_value=np.nan):
                 dtype = np.dtype(np.object_)
             fill_value = np.nan
 
+        if dtype == np.object_ or dtype.kind in ["U", "S"]:
+            # We treat string-like dtypes as object, and _always_ fill
+            #  with np.nan
+            fill_value = np.nan
+            dtype = np.dtype(np.object_)
+
     # returns tuple of (dtype, fill_value)
     if issubclass(dtype.type, np.datetime64):
-        try:
-            fill_value = tslibs.Timestamp(fill_value).to_datetime64()
-        except (TypeError, ValueError):
+        if isinstance(fill_value, datetime) and fill_value.tzinfo is not None:
+            # Trying to insert tzaware into tznaive, have to cast to object
             dtype = np.dtype(np.object_)
+        else:
+            try:
+                fill_value = tslibs.Timestamp(fill_value).to_datetime64()
+            except (TypeError, ValueError):
+                dtype = np.dtype(np.object_)
     elif issubclass(dtype.type, np.timedelta64):
         try:
             fv = tslibs.Timedelta(fill_value)
@@ -417,8 +427,6 @@ def maybe_promote(dtype, fill_value=np.nan):
     # in case we have a string that looked like a number
     if is_extension_array_dtype(dtype):
         pass
-    elif is_datetime64tz_dtype(dtype):
-        pass
     elif issubclass(np.dtype(dtype).type, (bytes, str)):
         dtype = np.object_
 

pandas/tests/dtypes/cast/test_promote.py

@@ -723,9 +723,6 @@ def test_maybe_promote_any_numpy_dtype_with_datetimetz(
     fill_dtype = DatetimeTZDtype(tz=tz_aware_fixture)
     boxed, box_dtype = box  # read from parametrized fixture
 
-    if dtype.kind == "M" and not boxed:
-        pytest.xfail("Comes back as M8 instead of object")
-
     fill_value = pd.Series([fill_value], dtype=fill_dtype)[0]
 
     # filling any numpy dtype with datetimetz casts to object
@@ -847,11 +844,6 @@ def test_maybe_promote_string_with_any(string_dtype, any_numpy_dtype_reduced, bo
     fill_dtype = np.dtype(any_numpy_dtype_reduced)
     boxed, box_dtype = box  # read from parametrized fixture
 
-    if boxed and box_dtype is None and fill_dtype.kind == "m":
-        pytest.xfail("wrong missing value marker")
-    if boxed and box_dtype is None and fill_dtype.kind == "M":
-        pytest.xfail("wrong missing value marker")
-
     # create array of given dtype; casts "1" to correct dtype
     fill_value = np.array([1], dtype=fill_dtype)[0]
 
@@ -914,9 +906,6 @@ def test_maybe_promote_object_with_any(object_dtype, any_numpy_dtype_reduced, bo
     fill_dtype = np.dtype(any_numpy_dtype_reduced)
     boxed, box_dtype = box  # read from parametrized fixture
 
-    if boxed and box_dtype is None and is_datetime_or_timedelta_dtype(fill_dtype):
-        pytest.xfail("wrong missing value marker")
-
     # create array of given dtype; casts "1" to correct dtype
     fill_value = np.array([1], dtype=fill_dtype)[0]