I had trouble making my numpy segfault on this one, because the `op` array was coming out with 3 or 4 leading zeros. Probably adding more `None`s to the call will make this more effective at catching a regression. 63 `None`s is the maximum you can give to `np.einsum` without it complaining about "too many arguments", so I would suggest:

    assert_raises(TypeError, np.einsum, *(None,)*63)