def testGetChebyschevLpf(self):
        time = range(500)
        fundamental = 8*arctan(1)/30
        noise = 8*arctan(1)/4
        
        input = time[:]
        for t in time:
            input[t]=cos(fundamental*t) + cos(noise*t)
            
        output = DigitalFilter.get_chebyschev_lpf(input, 20)

        self.assertEqual(len(input), len(output), 'good length')
        self.assertAlmostEqual(output[499], -1.15550766,msg='good Chebyschev')