Dashatize it has good tests to learn from. Click on "Show Kata Test Cases" (I can't link straight to there) and read how he does it. That's the general pattern; you can build on that if necessary.

Generating good random inputs can be complicated, and there are some gotcha's, but those'll probably be pointed out as you go along.

There are no published documents that take you beyond the basics really. Read tests and comments on others' kata and learn what you can do wrong. Writing tests is an art as much as a craft, and not everybody is good at it, so don't take anything anybody else does as gospel.

And never ever use Test.expect ! :P