Cheatsheet to test using Mocha, Chai and Sinon

This is a little cheatsheet with snnipets to create unit tests using Mocha test runner, Chai assertion library and Sinon (for spies and stubs).

How to set them up with mocha

To start to setup your tests you need to define a test suite using describe. These act like closures and you can even nest them.

describe('My feature test', function() {
    // ...
});

describe.only will ensure that only this test suite will run.

Mocha before, beforeEach, after, afterEach

You can use before these to setup and restore any test helpers or components. You can even call these agains in nested describe.

describe('My feature test', function() {
    let classToTest;
    beforeEach(function() {
        classToTest = new ClassToTest();
    });
    
    afterEach(function() {
        classToTest = null;
    });
});

Mocha only and skip

You use it to perform a test, it allows it.only will ensure that only this test will executed, it.skip will skip the test.

it.only('should be able to get valueA', function() {
    //..
});

it.skip('this test is going to be skipped', function() {
    //..
});

Mocha increase test timeout

Mocha handle done callback

it('mocha can done callback', function(done) {
    testSubject.getPromiseMethod().then(function(data) {
        expect(data).to.equal('Resolved!');
        done();
    });
});

Mocha return a promise

it('mocha can handle returned promises', function() {
    return testSubject.getPromiseMethod().then(function(data) {
        expect(data).to.equal('Resolved!');
    });
});

Chai contains and handleling arrays

    it('can check if it contains a method', function() {
        expect(testSubject.getArray()).include(2);
    });

Chai contains and handleling objects

it('can check if it contains element in object', function() {
    expect(testSubject.getObject()).include({one: 'a'});
});

Sinon spy a call count

cont numberOfCalls = spy.callCount;

Sinon spy a call arguments

const firstCallFirstArgumentValue = spy.args[0][0];

Sinon spy called with arguments

const booleanCalled = spy.withArgs('MY_FIRST_ARGUMENT').calledOnce;

Sinon stub a method

sinon.stub(objectToStub, 'propertyInObjectToStub').returns({
  propertyMethod: sinon.stub()
});

Then remember after the test is done to restore the origiinal object.

objectToStub.propertyInObjectToStub.restore();

Sinon stub an object

sinon.stub(objectToStub, 'propertyWeAreStubbing').value({
  propertyMethod: sinon.stub()
});