def test_error_operations():
q = Quantity(10, m)
p = Quantity(5, s)
raises(ValueError, lambda: q.add(p))
raises(TypeError, lambda: q.add(1))
raises(ValueError, lambda: q.sub(p))
raises(TypeError, lambda: q.sub(1))
def test_operations():
q = Quantity(10, m)
p = Quantity(5, s)
assert -q == Quantity(-10, m)
assert q.add(Quantity(20, m)) == Quantity(30, m)
assert q.add(Quantity(20, Unit(m.dim, 10))) == Quantity(30, Unit(m.dim, 11))
assert q.sub(Quantity(20, m)) == Quantity(-10, m)
assert q.sub(Quantity(20, Unit(m.dim, 10))) == Quantity(-10, Unit(m.dim, -9))
assert q.pow(2) == Quantity(10**2, m.pow(2))
assert q.mul(p) == Quantity(5*10, m.mul(s))
assert q.div(p) == Quantity(10/5, m.div(s))