def test_string_quantity_not_valid(self): self.assertFalse(valid_quantity("12dfg2"))
def test_neg_quantity_value_is_invalid(self): self.assertFalse(valid_quantity(-1))
def test_positive_quantity_value_is_valid(self): self.assertTrue(valid_quantity(3))
def test_nonetype_not_valid(self): self.assertFalse(valid_quantity(None))