It's important to us that legacy formatters keep working in rspec 3. @JonRowe has been making lots of good changes and has done a great job of providing a compatibility shim but I personally find it hard to definitively say whether or not legacy formatters still work. The probably do, but the changes are too large to say for sure without trying them.
Given that we may continue to evolve the base classes and formatter API, getting these under test with some regression tests would be beneficial. Here's my suggestion for doing that: let's pick the most popular formatters (nyancat, fivemat, fuubar, etc), and have a cucumber feature (which need not be published to relish; they are regression tests, not docs) that defines some examples in a background step, and then has a scenario per formatter that demonstrates that it works against the rspec 3 API. We'd need to lock the version to a version of those formatters written against rspec 2.x. This will give us a huge confidence boost that the custom formatters keep working.
Thoughts from others?
cool, I'll take a stab at this -- if I can get this in in the next couple days it'll give us much greater confidence in beta2.
Add some regression tests for some popular custom formatter gems.
Closing in favor of @1292.