def test_first_argument_not_number(self): self.assertEquals(subtract('asd', 2), 'error')
def test_second_argument_not_number(self): self.assertEquals(subtract(3, 'asd'), 'error')
def test_subtract_positive_and_negative(self): self.assertEquals(subtract(21, -7), 28)
def test_subtract_negative_and_positive(self): self.assertEquals(subtract(-7, 21), -28)
def test_subtract_negative_numbers(self): self.assertEquals(subtract(-3, -15), 12)
def test_subtract_negative_numbers2(self): self.assertEquals(subtract(-79, -19), -60)
def test_subtract_negative_and_zero(self): self.assertEquals(subtract(-33, 0), -33)
def test_subtract_zero_and_negative(self): self.assertEquals(subtract(0, -33), 33)
def test_subtract_zero_and_positive(self): self.assertEquals(subtract(0, 45), -45)
def test_subtract_positive_and_zero(self): self.assertEquals(subtract(45, 0), 45)
def test_subtract_zeros(self): self.assertEquals(subtract(0, 0), 0)
def test_subtract_positive_numbers2(self): self.assertEquals(subtract(111, 11), 100)
def test_subtract_positive_numbers(self): self.assertEquals(subtract(10, 6), 4)