invoice.coffee

window.CountCalculator=window.PriceCalculator=window.TaxCalculator=window.ShippingCaclulator = { 
  calculate: (num) -> (num == undefined ? 0 : num + 1) }

ChainsCalls = 
  chain: (dependencies, method) ->
    _(dependencies).inject((memo, dependency) ->            
      dependency[method](memo)
    , undefined)
    
Invoice = 
  build: ->
    ChainsCalls.chain([CountCalculator, PriceCalculator, TaxCalculator, ShippingCaclulator], "calculate")

invoice_spec.coffee

describe "ChainsCalls", ->
  Given -> @a = go: jasmine.createSpy().andReturn("foo")
  Given -> @b = go: jasmine.createSpy().when("foo").thenReturn("bar")
  When -> @result = ChainsCalls.chain([@a,@b], "go")
  Then -> expect(@result).toBe("bar")

describe "Invoice", ->
  When -> @result = Invoice.build()  
  Then -> expect(@result).toEqual(4)