def test_isub(x1, y1, x2, y2):
a = Vector_C(x1, y1)
b = Vector_C(x2, y2)
c = a.copy()
a -= b
assert a.x == c.x - b.x
assert a.y == c.y - b.y
if x1 != 0 and x2 != 0:
assert a.x != c.x
if y1 != 0 and y2 != 0:
assert a.y != c.y
a -= Vector_C(1, 1)
assert a.x == c.x - b.x - 1
assert a.y == c.y - b.y - 1
def test_iadd(x1, y1, x2, y2):
a = Vector_C(x1, y1)
b = Vector_C(x2, y2)
c = a.copy()
a += b
assert a.x == c.x + b.x
assert a.y == c.y + b.y
if x1 != 0 and x2 != 0:
assert a.x != x2
if y1 != 0 and y2 != 0:
assert a.y != y2
a += Vector_C(1, 1)
assert a.x == c.x + b.x + 1
assert a.y == c.y + b.y + 1
