This is useful to send HTTP requests (or their PSR-7 equivalents)
through the entire application's middleware stack (instead of
talking to specific controllers, which should be considered
implementation detail).
This testing package was initially a part of flarum/core, but was
extracted during the 0.1.0-beta.16 release cycle. The extraction was
made through git's filter-branch tool to preserve some useful history in
the repository.
