Explain Mocha's testing framework - describe(), it() and before()/etc hooks

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
// 2. `it()` is a test case
// 3. `before()`, `beforeEach()`, `after()`, `afterEach()` are hooks to run
// before/after first/each it() or describe().
//
// Which means, `before()` is run before first it()/describe()

// -----------------------------------------------------------------------------

// should.js is the preferred assertion library
var should = require('should');

// **Only 1 test case (in a nameless test suite)**
it('birds should fly', function(){
  /** here.should.be.tested
    * However, as long as no error within a it(),
    * it() is considered 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', function(){
  describe('earth', function(){
    describe('singapre', function(){
      it('birds should fly', function(){ /** ... */ })
    })
  })
})


// **2 test cases in 1 test suite**

// A common scenario.
describe('singapre', function(){
  it('birds should fly', function(){ /** ... */ })
  it('horse should gallop', function(){ /** ... */ })
})


// **Run once before the first test case**
describe('singapre', function(){
  before(function(){
    console.log('see.. this function is run ONCE only')
  })
  it('birds should fly', function(){ /** ... */ })
  it('horse should gallop', function(){ /** ... */ })
})


// **Run once before each test case**
describe('singapre', function(){
  beforeEach(function(){
    console.log('see.. this function is run EACH time')
  })
  it('birds should fly', function(){ /** ... */ })
  it('horse should gallop', function(){ /** ... */ })
})

// **2 test suites in a big test suite**

// A common scenario.
describe('earth', function(){
  describe('singapre', function(){
    it('birds should fly', function(){ /** ... */ })
  })
  describe('malaysia', function(){
    it('birds should soar', function(){ /** ... */ })
  })
})


// **before() can be applied to describe() too**
describe('earth', function(){
  before(function(){
    console.log('see.. this function is run ONCE only, before first describe()')
  })
  describe('singapre', function(){
    it('birds should fly', function(){ /** ... */ })
  })
  describe('malaysia', function(){
    it('birds should soar', function(){ /** ... */ })
  })
})


// **beforeEach() can be applied to describe() too**
describe('earth', function(){
  beforeEach(function(){
    console.log('see.. this function is run EACH time, before each describe()')
  })
  describe('singapre', function(){
    it('birds should fly', function(){ /** ... */ })
  })
  describe('malaysia', function(){
    it('birds should soar', function(){ /** ... */ })
  })
})

  context('with token', async function () {
    beforeEach(async function () {
      this.token = await SimpleToken.new();
    });

    it('requires a non-zero rate', async function () {
      await expectRevert(
        Crowdsale.new(0, wallet, this.token.address), 'Crowdsale: rate is 0'
      );
    });

    it('requires a non-null wallet', async function () {
      await expectRevert(
        Crowdsale.new(rate, ZERO_ADDRESS, this.token.address), 'Crowdsale: wallet is the zero address'
      );
    });

    describe('low-level purchase', function () {
        it('should log purchase', async function () {
          const { logs } = await this.crowdsale.buyTokens(investor, { value: value, from: purchaser });
          expectEvent.inLogs(logs, 'TokensPurchased', {
            purchaser: purchaser,
            beneficiary: investor,
            value: value,
            amount: expectedTokenAmount,
          });
        });

context
  before
  it

describe
  it

context
  beforeEach
  context
    beforeEach