Translate present test cases to hypothesis strategies

[BjoernLudwigPTB]

We have several tests in our test suite which implement some kind of randomised testing utilising numpy.random e.g. test_DFT.py. After having tried out hypothesis on our interpolation test suite and having such a pleasant experience using it and discovering some corner cases, which we actually did not think of, we should now try to apply it to all the other bits of out test suite.

We believe that this will benefit the trust in our algorithms.