wrong

https://github.com/sconover/wrong

Wrong provides a general assert method that takes a predicate block. Assertion failure messages are rich in detail. The Wrong idea is to replace all those countless assert_this, assert_that library methods which only exist to give a more useful failure message than "assertion failed". Wrong replaces all of them in one fell swoop, since if you can write it in Ruby, Wrong can make a sensible failure message out of it. Also provided are several helper methods, like rescuing, capturing, and d.