How do I stub node.js built-in fs during testing?

Question

I want to stub node.js built-ins like fs so that I don\'t actually make any system level file calls. The only thing I can think to do is to pass in fs

Answer 1

I like using rewire for stubbing out require(...) statements

Module Under test

module-a.js

var fs = require('fs')
function findFile(path, callback) {
  fs.readdir(path, function(err, files) {
     //Do something.
  })
}

Test Code

module-a-test.js

var rewire = require('rewire')
var moduleA = rewire('./moduleA')
// stub out fs
var fsStub = {
  readdir: function(path, callback) {
     console.log('fs.readdir stub called')
     callback(null, [])
  }
}
moduleA.__set__('fs', fsStub)
// call moduleA which now has a fs stubbed out
moduleA()