plate-spinning.js

// Subject under test
function download (path, cb) {
  get(path, function (er, value) {
    if (er) return cb(er)
    insert(value.id, value, function (er) {
      cb(er)
    })
  })
}

// Test
module.exports = {
  beforeEach: function () {
    post('/interests', {id: 42, interests: ['Ruby on Rails']}, function () {})
  },
  getsAndThenInserts: function (done) {
    download('/interests', function (er) {
      select(42, function (er, value) {
        assert.deepEqual(value, {id: 42, interests: ['Ruby on Rails']})
        done(er)
      })
    })
  }
}

// Fake production implementations to simplify example test of subject
var _ = require('lodash')
var resources = {}
function post (path, value, cb) {
  randomTimeout(function () {
    resources[path] = value
    cb(null)
  }, 10, 30)
}

function get (path, cb) {
  randomTimeout(function () {
    cb(null, resources[path])
  }, 15, 50)
}

var db = {}
function insert (id, value, cb) {
  randomTimeout(function () {
    db[id] = value
    cb(null)
  })
}

function select (id, cb) {
  randomTimeout(function () {
    cb(null, db[id])
  })
}

function randomTimeout (func, low, high) {
  setTimeout(func, _(low || 10).range(high || 100).sample())
}

// Exclude this test from CI, since it's erratic
if (process.env.CI) module.exports = {}