This will allow us to have global setup and teardown for tests.
For example, we can automatically clear caches after each test, to avoid
annoying intermittent failures like #1879 and #1886.
This is the (partially) documented public API for Homebrew.
The main class you should look at is the {Formula} class (and classes linked from there). That's the class that's used to create Homebrew formulae (i.e. package descriptions). Assume anything else you stumble upon is private.