def METHOD_NAME(self, cosmo_cls, cosmo):
    """Test Parameter ``w0``."""
    # on the class
    assert isinstance(cosmo_cls.w0, Parameter)
    assert "Dark energy equation of state" in cosmo_cls.w0.__doc__
    assert cosmo_cls.w0.unit is None
    # on the instance
    assert cosmo.w0 is cosmo._w0
    assert cosmo.w0 == self.cls_kwargs["w0"]