[WIP] Validate hooks existence

:+1: for using `is_expected` RSpec 3 syntax.

:-1: for asserting that something doesn't raise. This guarantees nothing about your code:

https://github.com/seattlerb/minitest/issues/159#issuecomment-8214938
https://github.com/seattlerb/minitest/issues/70
http://blog.zenspider.com/blog/2012/01/assert_nothing_tested.html

Worse than that, it makes your test more complicated by deferring the `subject` with a lambda.