`AVAVerify#testBody` should shrink and rerun tests on failure, and report the smallest failing test case. See `jsverify#check` as well as `jsverify#forall` for details. See [`Test`](https://github.com/avajs/ava/blob/854203a728c4dff3ea61a3bcf49f1dfae04c7657/lib/test.js#L103) for AVA internals that will need to be saved/modified/restored.
