It took a while, but we (hopefully) just completed our common acceptance test suite for RS server APIs (version 03 to 05).
You can use it to test your RS server’s REST API from the outside and see if it’s compatible with the remoteStorage spec(s). Next step will be testing Webfinger and eventually getting to a full suite including the auth step. But this is already pretty useful for the REST API part of RS.
If you find something that is missing or wrong, please don’t hesitate to open an issue or add/fix it and open a PR. Thanks!