Module Under test

Question

191

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

rated 0 times [ 198] [ 7] / answers: 1 / hits: 21158 / 11 Years ago, sat, march 30, 2013, 12:00:00

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 and all other built-ins as an argument to all of my functions to avoid the real fs from being used. This seems a little bit silly and creates a verbose function signature crowded with built ins as arguments.

var fs = require('fs');



function findFile(path, callback) {

  _findFile(fs, path, callback);

}



function _findFile(fs, path, callback) {

  fs.readdir(path, function(err, files) {

     //Do something.

  });

}

And then during testing:

var stubFs = {

  readdir: function(path, callback) {

     callback(null, []);

  }

};



_findFile.(stubFs, testThing, testCallback);

There's a better way than this right?

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simone

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2 Years ago

answered 11 Years ago sidneyh · Accepted Answer

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()