def test_period(self):
R = z = phi = 1 * _pc
v_R = v_z = v_phi = 1 * _kms
P = period(MWPotential2014, [R, z, phi], [v_R, v_z, v_phi])
orb = Orbit(vxvv=[R/_pc, v_R/_kms, v_phi/_kms, z/_pc, v_z/_kms, phi])
P_galpy = orb.Tp(pot=MWPotential2014, analytic=True) * _yr
diff = np.abs(2 * (P - P_galpy) / (P + P_galpy))
self.assertLess(diff, 0.1, msg="period returns incorrect period")
