stronger tests for _fixup_dates

Author: rcomer

lib/iris/tests/unit/plot/test__fixup_dates.py

@@ -23,6 +23,7 @@ def test_gregorian_calendar(self):
         unit = Unit("hours since 2000-04-13 00:00:00", calendar="gregorian")
         coord = AuxCoord([1, 3, 6], "time", units=unit)
         result = _fixup_dates(coord, coord.points)
+        self.assertIsInstance(result[0], datetime.datetime)
         expected = [
             datetime.datetime(2000, 4, 13, 1),
             datetime.datetime(2000, 4, 13, 3),
@@ -34,6 +35,7 @@ def test_gregorian_calendar_sub_second(self):
         unit = Unit("seconds since 2000-04-13 00:00:00", calendar="gregorian")
         coord = AuxCoord([1, 1.25, 1.5], "time", units=unit)
         result = _fixup_dates(coord, coord.points)
+        self.assertIsInstance(result[0], datetime.datetime)
         expected = [
             datetime.datetime(2000, 4, 13, 0, 0, 1),
             datetime.datetime(2000, 4, 13, 0, 0, 1),