def test_abcd_thru(self):
        """
        Thru has ABCD matrix of the form:
        [ 1  0 ]
        [ 0  1 ]
        """
        ntw = self.dummy_media.thru()
        npy.testing.assert_array_almost_equal(ntw.a[:,0,0], 1.0)
        npy.testing.assert_array_almost_equal(ntw.a[:,0,1], 0.0)
        npy.testing.assert_array_almost_equal(ntw.a[:,1,0], 0.0)
        npy.testing.assert_array_almost_equal(ntw.a[:,1,1], 1.0)