Cross-implementation test suite

[bates64]

Nice-to-have. Would work like the @decent/server test suite but should work with any compliant-with-spec server, checking that it implements everything it MUST implement and warning if anything that SHOULD be implemented is not.

[towerofnix]

This would be handy for sure - decent/server is good for testing the individual units of the server, which includes endpoints, but a dedicated test suite for checking the spec would be good.

[bates64]

^{oh and also let's not write it in js}