def test_center_of_mass(self):
sun = Oschi("Sun", (0, 0, 0), 1, (0, 0, 0), 0.2)
earth = Oschi("Earth", (1, 1, 1), 27 * 10**11, (0, 0, 0), 0.1)
universe = Universe(60, [sun, earth])
u = universe.center_of_mass(earth)
self.assertTrue((universe.center_of_mass(earth) == (0, 0, 0)).all())
