gistfile1.md

Setting Up Mocha For Testing

In this lesson we'll setup testing for the project using the Mocha test framework

The BDD Testing Style

The Mocha test framework allows you to write your tests in many different styles. We'll choose to write our tests using the BDD style and the "expect" syntax of the Chai assertion library.

An example test looks like:

var expect = require("chai").expect;
describe('Array', function(){
  before(function(){
    // ...
  });

  describe('#indexOf()', function(){
    it('should return -1 when not present', function(){
      expect([1,2,3].indexOf(4)).to.equal(-1);
    });
  });
});

Writing The First Test

Install both mocha and chai as development dependencies:

$ npm install mocha chai --save-dev
...
chai@1.9.1 node_modules/chai
├── assertion-error@1.0.0
└── deep-eql@0.1.3 (type-detect@0.1.1)

mocha@1.18.2 node_modules/mocha
├── diff@1.0.7
├── debug@0.7.4
├── growl@1.7.0
├── commander@2.0.0
├── mkdirp@0.3.5
├── jade@0.26.3 (commander@0.6.1, mkdirp@0.3.0)
└── glob@3.2.3 (inherits@2.0.1, graceful-fs@2.0.3, minimatch@0.2.14)

There's no test yet:

$ mocha
  0 passing (1ms)

The mocha command find files that match the pattern test/*.js and run the tests in those files. Let's Create the first test file at test/greet_spec.js:

var expect = require("chai").expect
describe('greet', function(){
  it("is a dummy success case", function(){
    expect(1).to.eql(1);
  });
});

Let's run mocha (with the -R option to get more detailed output):

$ mocha -R spec

  greet
    ✓ is a dummy success case

  1 passing (6ms)

Implement: Write the actual test cases for the greet function. There are two cases:

• your test file should require the greet module
• should greet a person by name
• should greet a person flirtatiously if drunk

Hint: Chai BDD API reference.

The test output should look like:

$ mocha -R spec

  greet
    ✓ should greet a person by name
    ✓ should greet a person flirtatiously if drunk
  2 passing (6ms)

spec helper

As your test suite grows bigger into multiple files, you might find it helpful to be able to share code across all files.

In our case instead of having to require expect in every test file, let's create a spec helper to load it.

Remove var expect = require("chai").expect from test/greet_spec.js. The test suite should now fail:

$ mocha

  ․․

  0 passing (4ms)
  2 failing

  1) greet should greet a person by name:
     ReferenceError: expect is not defined

  2) greet should greet a person flirtatiously if drunk:
     ReferenceError: expect is not defined

In test/support/helper.js add the following:

global.expect = require("chai").expect;

Let's run mocha again with the --require option to load the helper:

$ mocha --require test/support/helper
․․
  2 passing (4ms)

It works.

Question: How is var expect = ... different from global.expect = ...? Does it work if in helper.js you use var expect = require("chai").expect;

Hint: See global

mocha.opts

It's cumbersome to have to type --require test/support/helper everytime you run a test. You can set mocha's default options by creating the mocha.opts in the test directory.

In test/mocha.opts add:

--require test/support/helper
--reporter spec

Now you can run mocha without specifying options:

$ mocha
  greet
    ✓ should greet a person by name
    ✓ should greet a person flirtatiously if drunk
  2 passing (6ms)

You can also run the test suite as an npm task:

$ npm test
npm test
> greet@0.0.0 test /Users/howard/workspace/node-bootcamp/greet
> mocha
  greet
    ✓ should greet a person by name
    ✓ should greet a person flirtatiously if drunk
  2 passing (6ms)

Bonus

If you'd like to gain more experience using Mocha, you are encouraged to read Better CoffeeScript Testing With Mocha is a great tutorial that guides you through building a todo list using TDD.

It uses the should syntax instead of expect.

global will set up as global ver which can be share to all the test file, it will not work if in helper.js to set var = expect = require("chai").expect;