added pytest.fixture & whatsnew

Author: debnathshoham

doc/source/whatsnew/v1.4.0.rst

@@ -258,7 +258,7 @@ Groupby/resample/rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed bug in :meth:`SeriesGroupBy.apply` where passing an unrecognized string argument failed to raise ``TypeError`` when the underlying ``Series`` is empty (:issue:`42021`)
 - Bug in :meth:`Series.rolling.apply`, :meth:`DataFrame.rolling.apply`, :meth:`Series.expanding.apply` and :meth:`DataFrame.expanding.apply` with ``engine="numba"`` where ``*args`` were being cached with the user passed function (:issue:`42287`)
--
+- Bug in :meth:`pandas.DataFrame.ewm`, where non-float64 dtypes were silently failing (:issue:`42452`)
 
 Reshaping
 ^^^^^^^^^

pandas/tests/window/test_ewm.py

@@ -184,8 +184,7 @@ def test_ewma_times_adjust_false_raises():
 
 
 @pytest.mark.parametrize("func", ["mean", "std", "var"])
-@pytest.mark.parametrize("dtype", [np.float32, np.float16, np.float64, float, "float"])
-def test_float_dtype_ewma(dtype, func):
+def test_float_dtype_ewma(func, float_dtype):
     # GH#42452
     expected_mean = DataFrame(
         {
@@ -203,7 +202,9 @@ def test_float_dtype_ewma(dtype, func):
         }
     )
     expected_var = expected_std ** 2
-    df = DataFrame({0: range(5), 1: range(6, 11), 2: range(10, 20, 2)}, dtype=dtype)
+    df = DataFrame(
+        {0: range(5), 1: range(6, 11), 2: range(10, 20, 2)}, dtype=float_dtype
+    )
     e = df.ewm(alpha=0.5, axis=1)
     result = getattr(e, func)()
     expected = {