- This method, called from `brew extract` in the case of extraction from
third-party taps, was untested. This led to it breaking when we refactored
some of it to appease Sorbet (see PR 7933). If I make the same
(flawed) change here and run these tests, they fail.
- There's a fair bit going on here, but most of it is setup for
committing changes to more files, as we're testing operations on
multiple files in a Homebrew repo.
- I originally tried to write tests for `brew extract`, but that
required _a lot_ of refactoring because those tests (and their helper
methods) aren't designed for third-party taps - they rely on
`CoreTap`. So testing the underlying method is a better solution.
