prop_check 0.18.2

PropCheck allows you to do property-based testing, including shrinking. (akin to Haskell's QuickCheck, Erlang's PropEr, Elixir's StreamData). This means that your test are run many times with different, autogenerated inputs, and as soon as a failing case is found, this input is simplified, in the end giving you back the simplest input that made the test fail.