Strange fs.readFile behavior while testing CoffeeScript with Mocha/Chai

Question

Strange fs.readFile behavior while testing CoffeeScript with Mocha/Chai

Please consider I have the following CoffeeScript code:

class Foobar
    test: (path) ->
        fs = require 'fs'
        fs.readFile path, (err, data) ->
            console.log 'fs.readFile callback fired'

root = exports ? window
root.Foobar = Foobar

And the following test file for Mocha:

chai = require 'chai'
expect = chai.expect
chai.should()

{Foobar} = require '../source/foobar'

describe 'Foobar', ->
    foobar = null
    it 'does nothing', ->
        foobar = new Foobar
        foobar.test 'foobar.txt'

I run the test:

mocha --compilers coffee:coffee-script -R spec

Strangely for me console logs nothing. When I change my Coffee to this (added two lines at the end):

class Foobar
    test: (path) ->
        fs = require 'fs'
        fs.readFile path, (err, data) ->
            console.log 'fs.readFile callback fired'

root = exports ? window
root.Foobar = Foobar

foobar = new Foobar
foobar.test 'foobar.txt'

I run the test, and now console logs fs.readFile callback fired twice, as expected.

So, why console was empty in the first case?

node.js
coffeescript
mocha
fs
chai

Answer 1

It's possible that your tests are ending before the readFile callback is executed. The test method should accept a callback:

class Foobar
    test: (path, callback) ->
        fs.readFile path, (err, data) ->
            console.log 'fs.readFile callback fired'
            callback err, data

That way you can write your test to run asynchronously:

it 'calls callback', (done) ->
    foobar = new Foobar()
    foobar.test 'foobar.txt', done