Group related tests into files

[maclover7]

test.c is over four thousand lines long and is getting a little hard to parse... any objections to moving some related tests into separate files in a test/ directory?

@indutny @bnoordhuis

[bnoordhuis]

Personally, I'm -0.5. Long files don't really bother me and breakups are annoying with git blame. I also don't really enjoy reviewing huge diffs.

But it Fedor thinks it's a good idea, I won't block it.

[maclover7]

ping @indutny

[indutny]

+1 for this, sorry for delay. This may require writing a mini test framework, though.