[Cogito]

Thanks for that, it's a good snapshot of the current state of promises.

The readme in the repository has some good discussion around the different features you mention here, but it would be really interesting to see a discussion around the design of this library in counterpoint to the other options available. Some other time maybe!

With regards to the promise-tests, I think multiple implementations validate a concept, and a set of tests for a specification is much more useful when multiple implementations can pass it. If the specification is extended you have multiple implementations to compare the impact against, and if the implementations' behaviour differ in notable ways then you expose holes in the test suite.

Multiple implementations of a specification, particularly when they all pass a common test suite, is a good thing.