Test incorrect state transitions of promises

[jnicklas]

It seems like the first part of the Promises/A+ spec isn't tested:

A promise must be in one of three states: pending, fulfilled, or rejected.

When pending, a promise:
  may transition to either the fulfilled or rejected state.
When fulfilled, a promise:
  must not transition to any other state.
  must have a fulfillment value, which must not change.
When rejected, a promise:
  must not transition to any other state.
  must have a rejection reason, which must not change.

I wrote a promise implementation which passed all tests, but failed to protect against incorrect state transitions. It should be fairly simple to write these tests given the existing adapter interface, I think.

I'd be willing to write these tests, I just wanted to run this by you first before I spend the time on creating a pull request.

[ForbesLindesay]

How do you plan to add these tests... I'm pretty sure we already test for multiple resolve and multiple reject calls. Of course a promise could offer an additional API method called mutate() which let you mutate the state after it was resolved, but I can't see how we could test for that.

[briancavalier]

@jnicklas Could you point us to a specific example, possibly from your implementation. For example, does your promise implementation allow an implementation-specific way of observing (perhaps via a public promise.state property?) a promise's state? As @ForbesLindesay says, we can only test against the then API, since that's the only specified way to observe a promise.

If you can show an example, though, that might help us understand if there's a hole in the spec and tests. Thanks!

[briancavalier]

@jnicklas If you can provide more info or examples here, we're happy to continue the discussion. If we haven't heard from you in two days, we'll consider this resolved or a non-issue. Thanks!