Testing Deploy Functions Using Sinon.JS in Yaydoc

In yaydoc, we deploy the generated documentation to the GitHub pages as well as Heroku. It is one of the important functions in the source code. I don’t want to break the build in future by any unnoticed change, so I decided to write a test case for deploy function. But the deploy function had lot dependencies like child processes, sockets, etc. Also it is not a pure function, so there is no return object to assert the value. Then I decided to stub for child process to check whether the correct script was passed or not. In order to write stub I decided to use sinon js framework because it can be used for writing stubs, mocks and spies. One of the advantages with sinon is that it’ll work with any testing framework.

sinon.stub(require("child_process"), "spawn").callsFake(function (fileName, args) {
  if (fileName !== "./ghpages_deploy.sh" ) {
    throw new Error(`invalid ${fileName} invoked`);

  if (fileName === "./ghpages_deploy.sh") {
    let ghArgs = ["-e", "-i", "-n", "-o", "-r"];
    ghArgs.forEach(function (x)  {
      if (args.indexOf(x) < 0) {
        throw new Error(`${x} argument is not passed`);
  let process = {
    on: function (listenerId, callback) {
      if (listenerId !== "exit") {
        throw new Error("listener id is not exit");
  return process;

In sinon you can create s stub by passing the object in the first parameter and the method name in the second parameter to sinon’s stub method. After it returns an object, pass the function which you would like to replace with the “callFakes” function.

In above code, I wrote a simple stub which overwrites NodeJS child_process’s spawn method. So I passed the “child_process” module in the first parameter and “spawn” method name in the second parameter. You must check whether they are passing the correct deploy script and the correct parameter. So, I wrote a function which checks the condition and then pass the method to the callFakes method.

describe('deploy script', function() {
  it("gh-pages deploy", function() {
    deploy.deployPages(fakeSocket, {
      gitURL: "https://github.com/sch00lb0y/yaydoc.git",
      encryptedToken: crypter.encrypt("dummykey"),
      email: "[email protected]",
      uniqueId: "ajshdahsdh",
      username: "fossasia"

Finally test the deploy function by calling it. I use mocha as a testing framework. I have already written a blog on mocha. If you’re interested in mocha please check out this blog.