You can call Backbone.history.start() once. Multiple calls causes Backbone to throw an Error saying: “Backbone.history has already been started”.

You’ll hit this error when testing, if you have each test case set up your application, and your application’s setup includes starting Backbone:

App =
  initialize: (data) ->
    # ...
    if not Backbone.history.started?
      Backbone.history.start({pushState: true})
      Backbone.history.started = true

You solve this by calling Backbone.history.stop() prior to initializing your application:

describe "App", ->
  describe "#initialize", ->
    it "starts Backbone.history", ->
      Backbone.history.started = null
      Backbone.history.stop()
      sinon.spy(Backbone.history, "start")
      App.initialize {}

      expect(Backbone.history.start).toHaveBeenCalled()

      Backbone.history.start.restore()

Source

Addition of Backbone.history.stop()