Cool. I have one tiny philosophical niggle, which is that I like "arbitrary" more than "random" because it makes it clear that the data _could_ be chosen another way, such as an exhaustive test through a list of regressions, an exhaustive tests of all data smaller than some size, etc.

In other words "random" is an implementation detail while the _interface_ is "arbitrary" a.k.a. this means "for all X, the test should pass"