The blog of

"That's a funny looking warthog", a post about mocking Grunt [gruntMock is a simple mock for testing Grunt.js multi-tasks]

While writing the grunt-check-pages task for Grunt.js, I wanted a way to test the complete lifecycle: to load the task in a test context, run it against various inputs, and validate the output. It didn't seem practical to call into Grunt itself, so I looked around for a mock implementation of Grunt. There were plenty of mocks for use with Grunt, but I didn't find anything that mocked the API itself. So I wrote a very simple one and used it for testing.

That worked well, so I wanted to formalize my gruntMock implementation and post it as an npm package for others to use. Along the way, I added a bunch of additional API support and pulled in domain-based exception handling for a clean, self-contained implementation. As I hoped, updating grunt-check-pages made its tests simpler and more consistent.

Although gruntMock doesn't implement the complete Grunt API, it implements enough of it that I expect most tasks to be able to use it pretty easily. If not, please let me know what's missing! :)


For more context, here's part of the introductory section of

gruntMock is simple mock object that simulates the Grunt task runner for multi-tasks and can be easily integrated into a unit testing environment such as Nodeunit. gruntMock invokes tasks the same way Grunt does and exposes (almost) the same set of APIs. After providing input to a task, gruntMock runs and captures its output so tests can verify expected behavior. Task success and failure are unified, so it's easy to write positive and negative tests.

Here's what gruntMock looks like in a simple scenario under Nodeunit:

var gruntMock = require('gruntmock');
var example = require('./example-task.js');

exports.exampleTest = {

  pass: function(test) {
    var mock = gruntMock.create({
      target: 'pass',
      files: [
        { src: ['unused.txt'] }
      options: { str: 'string', num: 1 }
    mock.invoke(example, function(err) {
      test.equal(mock.logOk.length, 1);
      test.equal(mock.logOk[0], 'pass');
      test.equal(mock.logError.length, 0);

  fail: function(test) {
    var mock = gruntMock.create({ target: 'fail' });
    mock.invoke(example, function(err) {
      test.equal(err.message, 'fail');


For a more in-depth example, have a look at the use of gruntMock by grunt-check-pages. That shows off integration with other mocks (specifically nock, a nice HTTP server mock) as well as the testOutput helper function that's used to validate each test case's output without duplicating code. It also demonstrates how gruntMock's unified handling of success and failure allows for clean, consistent testing of input validation, happy path, and failure scenarios.

To learn more - or experiment with gruntMock - visit gruntMock on npm or gruntMock on GitHub.

Happy mocking!