def test_subtraction_of_negative_2_minus_negative_4(self):
first_number = -2
second_number = -4
calculator = Calculator("comum")
self.assertEqual(2, calculator.subtract(first_number, second_number))
def test_subtraction_of_0_minus_1(self):
first_number = 0
second_number = 1
calculator = Calculator("comum")
self.assertEqual(-1, calculator.subtract(first_number, second_number))