https://github.com/seattlerb/minitest really removed the FUD for me when i started learning Ruby and Rails. Its full of metaprogramming and fancy tricks but is also quite small, practical and informal in its style.

e.g. "assert_equal" is really just "expected == actual" at it's core but it uses both both a block param (a kind of closure) for composing a default message and calls "diff" which is a dumb wrapper around the system "diff" utility (horrors!). There is even some evolved nastiness in there for an API change that uses the existing assert/refute logic to raise an informative message. this is handled with a simple if and not some sort of complex hard-to-follow factory pattern or dependency injection misuse.

https://github.com/seattlerb/minitest/blob/master/lib/minite...