def save(self, doc):
        if doc.id:
            return self.update(doc)
        else:
            return self.insert(doc)
def test_critical_angle():
    m1 = Medium('m1', n=1)
    m2 = Medium('m2', n=1.33)
    assert ae(critical_angle(m2, m1), 0.85, 2)