fn-spy

creating spies for your functions

---

api

const spy = require('fn-spy')

spy(function[, thisArg])

function the function to be spied thisArg the this argument for the call (to be used with Classes or Objects)

methods

spy.calledCount() integer, returns the number of times a function as called

spy.calledWith() array, returns the arguments passed to the function

spy.getReturns() array, returns the output of the executed functions

spy.restore() function, restores the function to the initial state

spy an emitter function

const spyMyEmitter = spy.emitter() and will return the same methods as above

spy a callback function

const spyMyEmitter = spy.callback() and will return the same methods as above

examples

generic example

const spy = require('fn-spy')
 
function foo (...args) {
  return args.length
}
 
let spiedFn = spy(foo)
 
// calledCount
spiedFn()
spiedFn()
spiedFn.calledCount()// will return 2
 
// calledWith
spiedFn(1, 2, 3)
spiedFn.calledWith()// will return [[1, 2, 3]]
 
// restore
spiedFn = spiedFn.restore()// now spiedFn is retored to the initial state

emitter example

const EE = require('events')
const spy = require('fn-spy')
 
const myEmitter = new EE()
const spyEmitter = spy.emitter()
 
myEmitter.on('hey', spyEmitter)
 
myEmitter.emit('hey')
 
spyEmitter.calledCount()// will return 1
spyEmitter.calledWith()// will return [[]]

callback example

const spy = require('fn-spy')
 
const spyCallback = spy.callback()
 
 function someFunction (cb) {
    cb()
  }
 
someFunction(spyCallback)
 
spyCallback.calledCount()// will return 1
spyCallback.calledWith()// will return [[]]

Class / Object example

function BladeRunner () {
  this.sn = '9-9-0-6-9-4-7-X-B-7-1'
}
 
BladeRunner.prototype.getReplicant = function getReplicant () {
  return this.sn
}
 
const deckard = new BladeRunner()
const spy = fnSpy(deckard.getReplicant, deckard)
 
spy()// returns '9-9-0-6-9-4-7-X-B-7-1'
 
spy.calledCount()// will return 1
spy.calledWith()// will return [[]]
spy.getReturns()// will return ['9-9-0-6-9-4-7-X-B-7-1']
 

ISC License (ISC)