def METHOD_NAME(self):
    print('Testing double exponential')
    fn, params = hhfit.find_ratefn(self.v_array, self.dblexp)
    fnval = fn(self.v_array, *params)
    plt.plot(self.v_array, self.dblexp, 'y-', self.v_array,
             hhfit.double_exp(self.v_array, *self.p_dblexp), 'b--',
             self.v_array, fnval, 'r-.')
    self.assertEqual(hhfit.double_exp, fn)
    rms_error = np.sqrt(np.mean((self.dblexp - fnval)**2))
    print(params, rms_error)
    self.assertAlmostEqual(rms_error / max(self.dblexp), 0.0, places=3)
    plt.legend('Original dblexp %s, fitted %s' %(self.dblexp, fn))
    out = "__test_dblexponential.png"
    plt.savefig(out)
    print('Plot is saved saved to %s' % out)