Promise support

[TheLudd]

Mocha now has promise support. Would it be possible to also add it to mocha-given?
In mocha i can write:

describe 'myPromiseFunction', ->

  beforeEach -> someAsyncSetup()

  it 'shoud return "foo" async', -> 
    myPromiseFunction().then (result) ->
      result.should.equal 'foo'  

It would be awesome if mocha-given supported this:

describe 'myPromiseFunction', ->

  Given -> someAsyncSetup()
  When -> myPromiseFunction().then (@result) =>
  Then -> @result == 'foo'

[TheLudd]

@rendro @tandrewnichols
How about a comment on this idea? =)

[tandrewnichols]

Is that significantly different than

describe 'myPromiseFunction', ->

  Given -> someAsyncSetup()
  When (done) -> myPromiseFunction().then (@result) => done()
  Then -> @result == 'foo'

?

[TheLudd]

Yes. If your promise is rejected the error is not caught by your code. And writing catch statements leads to a lot of ceremony and space, especially in coffeescript

[tandrewnichols]

So what happens in mocha when the promise is rejected?

[TheLudd]

The test fails, like if you pass an error to done done(e). And the promise error is a part of the log.

[tandrewnichols]

And I assume it just hangs in mocha-given . . . ? But you mostly want to avoid having to write

When (done) -> myPromiseFunction()
  .success (@result) => done()
  .error (@result) => done()

Is that correct? (Incidentally, I think that syntax may only work in later versions of coffeescript, so the implementation might depend on what version you're using.)

I'm probably the wrong one to make a decision on this, not only because this isn't actually my library, but also because I almost never use promises, so familiarity there is not as high.

[TheLudd]

Yes I want to avoid that. I think it makes a big difference. Mostly because if it worked, the async call and result fetching could be put on one single line and I think that is a big win.

[TheLudd]

I mean, if i just want to avoid hitting the keyboard I could solve that with snippets in my editor but supporting promises makes the code more readable IMHO

[tandrewnichols]

Well, I'm a little unclear how mocha-given could hack into the promise mechanism (or how mocha pulls it off). Maybe @rendro will have a better understanding. Or if you know . . . open a PR :)

[rendro]

Hey, I guess we would need to look into the mocha code to understand how they implement promises and how we can use that behaviour to support promises in mocha-given.

I have the feeling this could lead to a major rewrite of the module ;)
Let's do this!

[TheLudd]

I think that all you need to do for it to work is to take what is returned from the Given/When function and make sure it is returned in the before funtion that is added to the suite. If it is a promise, mocha will handle it.

[TheLudd]

Guys, I solved this by writing my own version of Given When Then from scratch.... https://github.com/TheLudd/mocha-gwt