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.
Part of https://github.com/vector-im/element-web/issues/21972. Eventually I want to replace the whole of the current `Crypto` implementation with an alternative implementation, but in order to get from here to there, I'm factoring out a common interface which will be implemented by both implementations.
I'm also determined to fix the problem where the innards of the crypto implementation are exposed to applications via the `MatrixClient.crypto` property.
It's not (yet) entirely clear what shape this interface should be, so I'm going with a minimal approach and adding things as we know we need them. This means that we need to keep the old `client.crypto` property around as well as a new `client.cryptoBackend` property. Eventually `client.crypto` will go away, but that will be a breaking change in the js-sdk.
Richard van der Hoff