def METHOD_NAME(mdef):
    nM = ccl.halos.MassFuncWatson13(mass_def=mdef)
    for m in MS:
        n = nM(COSMO, m, 0.9)
        assert np.all(np.isfinite(n))
        assert np.shape(n) == np.shape(m)
    for m in MS:
        n = nM(COSMO, m, 0.1)
        assert np.all(np.isfinite(n))
        assert np.shape(n) == np.shape(m)