We have two similar tests with the same name, ContextAndHeaderTransportTests.
They shared lots of common code so I extracted much of it into
ActionRecordingPlugin, a plugin which records all action requests for later
inspection.
I also removed all the warnings from both tests. That made lang-mustache
compile cleanly without any custom -Xlint so I removed those. To remove
the warnings I had to add type parameters to ActionFilter which seemed
like a good idea anyway.