Add assertion that expected[0] is not NaT

Author: makbigc

pandas/tests/series/test_constructors.py

@@ -985,6 +985,7 @@ def test_fromIndex(self, src):
         expected = src.copy(deep=True)
         prod = Series(src)
         prod[::3] = NaT
+        assert expected[0] is not NaT
         tm.assert_index_equal(src, expected)
 
     # https://github.com/pandas-dev/pandas/issues/22698