The permutations are tested in the test that compares the results to those of a .npz file, the one that you do not like.
I admit that the permutations are not intensively tested and that it is a problem. But I doubt there is a simple way to reproduce the permutations values without copying the code that we actually want to test: I do not know any Python implementation of the permutation scheme that we use in the standard packages. Although way the data are permuted can be determined from the value of `random_state`, we actually work with orthonormalized residuals of two initial OLS fits. Such a state is hard to obtain with a code that it not at least as complex as the code we want to actually test.