However, the test suite that you are required to use is missing, since the website has gone down. I want to answer the challenge, so what should I do?
What should I do with my answer?
The real question is, what should we do with the challenge?
If new answers cannot be scored anymore because some outside resource became unavailable, I see only two possible courses of action.
Replace the broken link with a working one.
In this particular case, the Wayback Machine appears to have mirrored the resource here: https://web.archive.org/web/20161114211602/http://stat.fsu.edu/pub/diehard/
Close the challenge, as it no longer has a winning criterion.