followup to pandas-dev#28289

Author: jbrockmendel

pandas/tests/reductions/test_reductions.py

@@ -299,15 +299,6 @@ def test_timedelta_ops(self):
         result = td.to_frame().std()
         assert result[0] == expected
 
-        # invalid ops
-        for op in ["skew", "kurt", "sem", "prod", "var"]:
-            msg = "reduction operation '{}' not allowed for this dtype"
-            with pytest.raises(TypeError, match=msg.format(op)):
-                getattr(td, op)()
-
-            with pytest.raises(TypeError, match=msg.format(op)):
-                getattr(td.to_frame(), op)(numeric_only=False)
-
         # GH#10040
         # make sure NaT is properly handled by median()
         s = Series([Timestamp("2015-02-03"), Timestamp("2015-02-07")])
@@ -318,6 +309,22 @@ def test_timedelta_ops(self):
         )
         assert s.diff().median() == timedelta(days=6)
 
+    @pytest.mark.parametrize("opname", ["skew", "kurt", "sem", "prod", "var"])
+    def test_invalid_td64_reductions(self, opname):
+        s = Series(
+            [Timestamp("20130101") + timedelta(seconds=i * i) for i in range(10)]
+        )
+        td = s.diff()
+
+        msg = "reduction operation '{op}' not allowed for this dtype"
+        msg = msg.format(op=opname)
+
+        with pytest.raises(TypeError, match=msg):
+            getattr(td, opname)()
+
+        with pytest.raises(TypeError, match=msg):
+            getattr(td.to_frame(), opname)(numeric_only=False)
+
     def test_minmax_tz(self, tz_naive_fixture):
         tz = tz_naive_fixture
         # monotonic