[SciPy-Dev] How to get "correct" values for unit tests

Hi, while working on the tests for the new scipy.interpolate.{Smooth,LSQ}SphereBiavariateSpline classes, I'm wondering how to come up with sensible TRUE example values to test against. In the case mentioned (see https://github.com/scipy/scipy/pull/192), I simply wrapped a routine (sphere.f) from FITPACK. So I could write a direct FORTRAN program using sphere.f to calculate some "TRUE" values. However, that would just check that the wrapping actually works. Is this considered enough? Ultimately, I would like a test to assure that the results are correct. But for that, wouldn't it be "better" (whatever that means) to use a different library to calculate the TRUE results? Sorry, this might be a confusing email. Cheers, Andreas.