Implement tests to prevent certain operations from taking too long

[cloudburstwan]

During discussion of #502, both me and @Ixrec thought independently of the idea of adding tests to allow us to determine how long things would take with ratelimits put into account, and that if something took too long, the test should fail. This would encourage code to be written with at least some efficiency.

I personally don't know whether it's a good idea from a testing perspective, but it feels like it'd be a good idea.