Yes, those are potentially infinite, but a core set would be useful. As ambiguities come up, publish an addendum for clarification, and eventually, as the exceptions accumulate, a version step.

I don't understand how anyone can write a spec without concrete examples of pass/fail in their head. Perhaps there could be an informal example/counterexample syntax for those writing RFCs, which could be extracted into the 1.0 test suite.

The test suite must be a single open source repo, that accumulates acceptable edge cases until the relevant informed adults can make a call about revising the spec.

There has to be one approved, sanctioned, well-known and monitored test suite repo. It cannot be shrugged off into a free-for-all that makes it impossible to find a single canonical test suite. The interwebs are big and conflicted.

See Imre Lakatos 'Proofs and Refutations' for how this evolves.