These specify that they are needed by the test block. This can be
combined with `:build` to ensure that this formula isn't uninstalled
by `brew test-bot` when running `test do` blocks on our CI.
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.