twitter.coffee

credentials = stub()
twitter = stub()

describe "Twitter, wrapper for ntwitter", ->

  # just declare an undefined variable so it can get picked up later
  # with closure scope.
  # other alternative i can think of: twitter = "" # empty string or other val
  # e.g. what I want is just a `var twitter;`
  {twitter} = {}

  beforeEach ->
    twitter = new Twitter( credentials, twitterLib )

  it "creates the twitter library with credentials", ->
    expect(twitterLib).to.have.been.calledWith credentials

  it "stores the created twitter library", ->
    expect(twitter).to.have.ownProperty 'twitterLib'

Normally a test framework lets you assign @twitter = new Twitter credentials, twitterLib, so you don't need to share that scoped variable.

I'd just do twitter = null though if your testing framework doesn't work like that.

Also, I can't think of any case where I'd want an undefined variable floating around getting re-assigned in application code.

It's only in the test code, as a test variable. People also use closures for mocking private javascript variables, but I dislike using private variables most of the time.

Just me doing dumb things to save typing an @ symbol. :P

Mocha does support using this for each spec, and for async tests, actually makes more sense than the thing I want to do, because each spec would have its own instance variable, versus getting overwritten by other tests.