'For fun, a more complicated example of addition and subtraction.'

def test_complicated_addition_subtraction(self):

    dm0 = u.Unit(u'DM', (1.0 / ((4.0 * np.pi) * ((10.0 * u.pc) ** 2))))
    DMmag = u.mag(dm0)
    m_st = (10.0 * u.STmag)
    dm = (5.0 * DMmag)
    M_st = (m_st - dm)
    assert M_st.unit.is_equivalent(((u.erg / u.s) / u.AA))
    assert (np.abs(((M_st.physical / (((m_st.physical * 4.0) * np.pi) * ((100.0 * u.pc) ** 2))) - 1.0)) < 1e-15)
