def test_units_match():
class XxxMoney(int):
currency = 'XXX'
m1 = Money(1)
m2 = Money(2)
m3 = Money(3)
m3._currency = 'XXX'
m4 = XxxMoney(4)
assert m1._units_match(m2)
assert not m1._units_match(m3)
assert m3._units_match(m4)
