'Test addition & subtraction'

def testAddition(self):

    a1 = A(sq_m=100)
    a2 = A(sq_m=200)
    a3 = (a1 + a2)
    self.assertEqual(a3.sq_m, 300)
    a3 += a1
    self.assertEqual(a3.sq_m, 400)
    a4 = (a1 - a2)
    self.assertEqual(a4.sq_m, (-100))
    a4 -= a1
    self.assertEqual(a4.sq_m, (-200))
    with self.assertRaises(TypeError):
        a5 = (a1 + 1)
        self.fail('Area    +    number    should    raise    TypeError')
    with self.assertRaises(TypeError):
        a5 = (a1 - 1)
        self.fail('Area    -    number    should    raise    TypeError')
    with self.assertRaises(TypeError):
        a1 += 1
        self.fail('Area    +=    number    should    raise    TypeError')
    with self.assertRaises(TypeError):
        a1 -= 1
        self.fail('Area    -=    number    should    raise    TypeError')
