Actually, no, the function values are implicitly tested by cheby1, butter, etc.  so the only thing that needs to be tested on the prototype functions themselves is their output type, not their values.

However, these functions have different parameters, so `for func in list` won't work.  How about this?

        for func in (buttap, 
                     besselap, 
                     lambda N: cheb1ap(N, 1), 
                     lambda N: cheb2ap(N, 20),
                     lambda N: ellipap(N, 1, 20)):
            for N in range(7):
                z, p, k = func(N)
                assert_(isinstance(z, np.ndarray))
                assert_(isinstance(p, np.ndarray))