Added check for FutureWarning

Author: Chris Bertinato

pandas/tests/scalar/timedelta/test_timedelta.py

@@ -1,6 +1,5 @@
 """ test the scalar Timedelta """
 from datetime import timedelta
-from warnings import catch_warnings, simplefilter
 
 import numpy as np
 import pytest
@@ -290,10 +289,10 @@ def test_iso_conversion(self):
         assert to_timedelta('P0DT0H0M1S') == expected
 
     def test_nat_converters(self):
-        with catch_warnings():
-            simplefilter("ignore", FutureWarning)
-
+        with tm.assert_produces_warning(FutureWarning):
             assert to_timedelta('nat', box=False).astype('int64') == iNaT
+
+        with tm.assert_produces_warning(FutureWarning):
             assert to_timedelta('nan', box=False).astype('int64') == iNaT
 
     @pytest.mark.parametrize('units, np_unit',