FinishedPromise.install() replaces native Promise

[aslakhellesoy]

This is an attempt to provide a simple mechanism to replace the native Promise with FinishedPromise.

The rationale behind this is to be able to force 3rd party libraries using Promise to use FinishedPromise in tests.

I haven't tested this with any 3rd party libraries, so this PR is just to start the discussion. Do you think this would work?

[aslakhellesoy]

I just remembered now what you told me earlier @joshski - the problem is with async await code - it's harder to make that use FinishedPromise ?

[joshski]

Yeah async/await is a problem that I'm not sure how to work around yet 😤

Also I wondered whether this was worth doing or not bearing in mind load order: a library may have already made a reference to Promise before FinishedPromise.install is called...

[aslakhellesoy]

Relevant: nodejs/CTC#7

[aslakhellesoy]

a library may have already made a reference to Promise before FinishedPromise.install is called

You mean stdlib library or 3rd party npm module?
I think it's possible to have FinishedPromise.install() before any other 3rd party npm modules are loaded - that could be done in the test runner's entry point coudn't it?

[joshski]

that could be done in the test runner's entry point coudn't it?

Sure, in theory. When I tried that in some early tests with mocha, I didn't have much luck. I forget exactly why, maybe it had something to do with the way mocha loaded before tests, or maybe it was some third-party library.

In the end, inconvenient as it may be, I think we may need to remember how to pass stuff in, if we are serious about separating the sync from the async :)

[aslakhellesoy]

I think I've come up with an acceptable workaround for async - await. WDYT @joshski ?

[joshski]

Wow, great idea!

Looks promising 😆 -- will have a play with this as soon as I can