Explain Mocha's testing framework - describe/it/before/beforeEach etc.

mocha-guide-to-testing.js

/* -----------------------------------------------------------------------------

    ### Mocha Guide to Testing ###

    Objective is to explain `describe()`, `it()`, and `before()`/etc hooks.

      1.  `describe()` is merely for grouping, which you can nest as deep
          as is required.

      2.  `it()` is a test case.

      3.  `before()`, `beforeEach()`, `after()`, `afterEach()` are hooks
          that get called before/after first/each `it()` or `describe()`.

    Which means that `before()` is run before the first `it()`/`describe()`.

----------------------------------------------------------------------------- */

// should.js is the preferred assertion library
import should from 'should'


// **Only 1 test case (in a nameless test suite)**
it('birds should fly', () => {
  // As long as no error is thrown, it() is considered to have PASSED */
})


// **Only 1 test case, but nested 3-level deep**

// describe() are:
// - commonly known as test suites, which contains test cases
// - merely groups, and you can have groups within groups
describe('galaxy', () => {
  describe('earth', () => {
    describe('singapre', () => {
      it('birds should fly', () => { /** ... */ })
    })
  })
})


// **2 test cases in 1 test suite**
describe('singapre', () => {
  it('birds should fly', () => { /** ... */ })
  it('horse should gallop', () => { /** ... */ })
})


// **Run once before the first test case**
describe('singapre', () => {
  before(() => {
    console.log('see.. this function is run ONCE only')
  })

  it('birds should fly', () => { /** ... */ })
  it('horse should gallop', () => { /** ... */ })
})


// **Run once before each test case**
describe('singapre', () => {
  beforeEach(() => {
    console.log('see.. this function is run EACH time')
  })

  it('birds should fly', () => { /** ... */ })
  it('horse should gallop', () => { /** ... */ })
})


// **2 test suites in a big test suite**
describe('earth', () => {
  describe('singapre', () => {
    it('birds should fly', () => { /** ... */ })
  })

  describe('malaysia', () => {
    it('birds should soar', () => { /** ... */ })
  })
})


// **before() can be applied to describe() too**
describe('earth', () => {
  before(() => {
    console.log('see.. this function is run ONCE only, before first describe()')
  })

  describe('singapre', () => {
    it('birds should fly', () => { /** ... */ })
  })

  describe('malaysia', () => {
    it('birds should soar', () => { /** ... */ })
  })
})


// **beforeEach() can be applied to describe() too**
describe('earth', () => {
  beforeEach(() => {
    console.log('see.. this function is run EACH time, before each describe()')
  })

  describe('singapre', () => {
    it('birds should fly', () => { /** ... */ })
  })

  describe('malaysia', () => {
    it('birds should soar', () => { /** ... */ })
  })
})