testdouble/src/when.js

A minimal test double library for TDD with JavaScript

import _ from './wrap/lodash'
import callback from './callback'
import isCallback from './matchers/is-callback'
import calls from './store/calls'
import log from './log'
import stubbings from './store/stubbings'
import tdConfig from './config'
import cloneDeepIfPossible from './clone-deep-if-possible'
import symbols from './symbols'

export default function when (__userDoesRehearsalInvocationHere__, config = {}) {
  return ({
    thenReturn (...stubbedValues) {
      return addStubbing(stubbedValues, config, 'thenReturn')
    },
    thenCallback (...stubbedValues) {
      return addStubbing(stubbedValues, config, 'thenCallback')
    },
    thenDo (...stubbedValues) {
      return addStubbing(stubbedValues, config, 'thenDo')
    },
    thenThrow (...stubbedValues) {
      return addStubbing(stubbedValues, config, 'thenThrow')
    },
    thenResolve (...stubbedValues) {
      warnIfPromiseless()
      return addStubbing(stubbedValues, config, 'thenResolve')
    },
    thenReject (...stubbedValues) {
      warnIfPromiseless()
      return addStubbing(stubbedValues, config, 'thenReject')
    }
  })
}

function addStubbing (stubbedValues, config, plan) {
  const last = calls.pop()
  ensureRehearsalOccurred(last)
  ensureCloneableIfCloneArgs(last, config)
  _.assign(config, { plan })
  stubbings.add(last.testDouble, concatImpliedCallback(last.args, config), stubbedValues, config)
  return last.testDouble
}

function ensureRehearsalOccurred (last) {
  if (!last) {
    return log.error('td.when', `\
No test double invocation call detected for \`when()\`.

  Usage:
    when(myTestDouble('foo')).thenReturn('bar')\
`
    )
  }
}

function ensureCloneableIfCloneArgs (last, config) {
  if (config.cloneArgs && cloneDeepIfPossible(last.args) === symbols.uncloneable) {
    return log.error('td.when', `\
Failed to deep-clone arguments. Ensure lodash _.cloneDeep works on them
`)
  }
}

function concatImpliedCallback (args, config) {
  if (config.plan !== 'thenCallback') {
    return args
  } else if (!_.some(args, isCallback)) {
    return args.concat(callback)
  } else {
    return args
  }
}

function warnIfPromiseless () {
  if (tdConfig().promiseConstructor == null) {
    log.warn('td.when', `\
no promise constructor is set, so this \`thenResolve\` or \`thenReject\` stubbing
will fail if it's satisfied by an invocation on the test double. You can tell
testdouble.js which promise constructor to use with \`td.config\`, like so:

  td.config({
    promiseConstructor: require('bluebird')
  })\
`)
  }
}