Examples of testing promise controller steps with and without bind

bind-no-bind-test-examples.js

const steps = {
    stepBind(req, foo) {
        // bla
    },

    stepNoBind: (req) => (foo) => {
        // bla
    }
}

// controller
app.get('/foo', (req, res) => {
    q({})
        .then(steps.stepBind.bind(null, req))
        .then(steps.stepNoBind(req))
        .catch(errorHandler)
})


// tests
import sinon from 'sinon'

import Steps from './controller-steps'
import Controller from './controller'

describe('controller', () => {
    let req,
        sandbox

    beforeEach(() => {
        req = {}

        sandbox = sinon.sandbox.create()

        sandbox.stub(Steps, 'stepNoBind')

        // can't just stub `stepBind`, because the called function is the the *return* of `.bind`
        // need to stub `.bind` instead
        sandbox.stub(Steps.stepBind, 'bind')

        Controller.get(req)
    })

    afterEach(() => {
        sandbox.restore()
    })

    describe('#get', () => {
        it('passes `req` to `stepBind`', () => {
            sinon.assert.calledWith(Steps.stepBind.bind, null, req)
        })

        it('passes `req` to `stepNoBind`', () => {
            sinon.assert.calledWith(Steps.stepNoBind, req)
        })
    })
})

function step(req, cb) {
  //...
}

function wrapper(req) {
  return (cb) => { step(req, cb); }
}

// controller
app.get('/foo', (req, res) => {
    async([
      step.bind(null, req),
      wrapper(req)
    ], finalize);

  function finalize() { 
    //... 
  }
})

Agora são equivalentes o wrapper e bind.