def METHOD_NAME(self):
    min_mags = [2.4, 6.5, 6.7]
    max_mags = [2, 6.5, 7.3]
    bin_widths = [0.4, 0.1, 1.0]
    for min_mag, max_mag, bin_width in zip(min_mags, max_mags, bin_widths):
        exc = self.assert_mfd_error(
            TaperedGRMFD,
            min_mag=min_mag, max_mag=max_mag, corner_mag=1.5,
            bin_width=bin_width, a_val=1, b_val=0.2
        )
        error = 'maximum magnitude %g must be higher ' % max_mag + \
                'than minimum magnitude %g by ' % min_mag + \
                'bin width %g at least' % bin_width
        self.assertEqual(str(exc), error)