def test(self): self.assertIsNotNone(VARIANCE.units_func) mul = mock.Mock(return_value=mock.sentinel.new_unit) units = mock.Mock(__mul__=mul) new_units = VARIANCE.units_func(units) # Make sure the VARIANCE units_func tries to square the units. mul.assert_called_once_with(units) self.assertEqual(new_units, mock.sentinel.new_unit)