how do I assert that a function was called?

Question

how do I assert that a function was called?

I have a Goat class:

class Goat
  constructor: (@headbutt) -> 
    @isCranky = true

  approach: -> 
    if @isCranky
      @headbutt()

I'd like to write a Mocha test to assert that headbutt() was called if isCranky is true and approach is called.

The only explanation I can find for this is in Ruby. Tried translating it, but failed. How can I assert that the correct function was called? I think I can solve it in a hacky way, but would rather learn the right way. Suggestions?

node.js
coffeescript
mocha

Answer 1

How about?

describe 'Goat', ->
  it 'should call headbutt when approached', ->
    headbuttCalled = no
    headbutt = -> headbuttCalled = true
    goat = new Goat headbutt

    goat.approach()

    assert headbuttCalled

If you find yourself repeating many times this pattern of testing whether a function was called, you'd probably want to use something like SinonJS, which provides a "spy" construct:

headbutt = sinon.spy()
goat = new Goat headbutt

goat.approach()

assert headbutt.called