def METHOD_NAME(self):
    exc = self.assert_mfd_error(
        YoungsCoppersmith1985MFD,
        min_mag=-4.0, b_val=1.0, char_mag=6.0, char_rate=0.001,
        bin_width=0.1
    )
    self.assertEqual(str(exc), 'minimum magnitude must be positive')
    exc = self.assert_mfd_error(
        YoungsCoppersmith1985MFD,
        min_mag=0.0, b_val=1.0, char_mag=6.0, char_rate=0.001,
        bin_width=0.1
    )
    self.assertEqual(str(exc), 'minimum magnitude must be positive')