I became sufficiently annoyed with matrix-mock-request that I decided to replace it with fetch-mock, which is what we use in matrix-react-sdk and is generally more powerful, easier to use, and actually maintained.
Unfortunately, we have a TestClient utility which is widely used and quite tightly integrated with matrix-mock-request. It wasn't going to be possible to change TestClient without changing all the tests that use it.
I also don't find TestClient particularly easy to use - it does a lot of stuff which I'm not convinced ought to be done for every single test.
So... I've introduced a couple of new classes (SyncResponder, E2EKeyReceiver) which do some of the useful bits of TestClient, but in a more granular way, and have switched crypto.spec.ts over so that rather than instantiating a TestClient for each test, it creates a MatrixClient directly and intercepts the endpoints necessary.
