Minitest is maintained by Seattle.rb’s Ryan Davis.
In ~2005, Ryan was tasked with taking over maintainer-ship of test-unit only to realize how much code there was to maintain and how daunting it was to deal with it all.
Minitest was started in October 2006 with a simple thought experiment: “how hard could it be to replace ‘all’ of test-unit?”. In just about an hour of time and 99 lines of ruby, he got all of his various projects’ test suites up and passing.
Eventually, minitest expanded to include: a full assertion library; minitest/spec, minitest’s answer to “how hard it is to do BDD?”; minitest/mock, to provide both mocking and stubbing API; and minitest/benchmark, to provide hardware-independent performance testing.