1. Install mocha: npm i mocha --save-dev (-dev: this lib use only on dev mood)
2. Create basic function for test (utils.js)
3. Create test class for that (utils.test.js)
4. Edit test line in package.json: "test": "mocha */.test.js"
5. Run npm test
6. To auto restart tests use: nodemon --exec "npm test"
7. In commit 5: "test-watch":"nodemon --exec "npm test"" Run npm run test-watch
8. Adding Assertion library:(mjackson/expect) to install this use: npm install [email protected] --save-dev
   

it('should add two numbers', ()=>{
  var res = utils.add(55,5);

  if(res !== 60){
		throw new Error(`Expect 60 but got ${res}`);
	}

});

it('sholud add one number',()=>{
    var res = utils.squre(3);

    expect(res).toBe(9).toBeA('number');

});

** when we working with object we need to use toEqual method .for objects toBe not working**

expect({name:"Shehan"}).toEqual({name:"Shehan"});
expect({name:"Shehan"}).toNotEqual({name:"Gamage"});

9. Asynchronous code testing with mocha. when we using async function we need to tell mocha that function is a async function. for that we can use done()

   module.exports.asynAdd = (a, b, callback)=>{
     setTimeout(()=>{
       callback(a+b);
     },1000);
   };
   

   it('should async add two numbers',(done)=>{
       utils.asynAdd(3, 4, (sum)=>{
         expect(sum).toBe(7).toBeA('number');
         done();
       });
   });
   

10. Testing Express applications with supertest and mocha.

    1. install Express and create server.js.
    2. install (supertest) npm install supertest --save-dev
    3. Create server.test.js file.

11. Organizing test with describe(). using describe() we can organize out testing code

    describe('sometext', ()=>{
      //add test functions
      //add test functions
      //add test functions
      });
    

12. Test spies

13. Using rewire with spies npm install rewire --save-dev