Alys/increase tests

[alysbrooks]

Increasing the test-suite find some errors we didn't already, so the threshold should be raised, at least sometimes.

I still need to decide whether to fix the failing tests or to.

I might also revise the tests a bit—I think we can use gen/such-that instead of for-all, :let, and :when.

[alysbrooks]

I should also look at replacing gen-carefully with such-that, too.

[alysbrooks]

A big issue here is that our generator seems to be generating characters that mess up a terminal, which makes it difficult to work with the output.