add test cases

Author: lostella

pandas/tests/scalar/timestamp/test_arithmetic.py

@@ -97,12 +97,15 @@ def test_addition_subtraction_types(self):
         assert type(ts - td64) == Timestamp
 
     @pytest.mark.parametrize('freq, td, td64', [
+        ('S', timedelta(seconds=1), np.timedelta64(1, 's')),
+        ('min', timedelta(minutes=1), np.timedelta64(1, 'm')),
+        ('H', timedelta(hours=1), np.timedelta64(1, 'h')),
         ('D', timedelta(days=1), np.timedelta64(1, 'D')),
         ('W', timedelta(weeks=1), np.timedelta64(1, 'W')),
         ('M', None, np.timedelta64(1, 'M'))
     ])
     def test_addition_subtraction_preserve_frequency(self, freq, td, td64):
-        ts = Timestamp('2014-03-05', freq=freq)
+        ts = Timestamp('2014-03-05 00:00:00', freq=freq)
         original_freq = ts.freq
 
         with tm.assert_produces_warning(FutureWarning):