jest intro

	
  mkdir getting-started-with-jest && cd $_
  npm init -y
  npm i jest --save-dev
  
  in package.json
    "scripts": {
    "test": "jest"
  },

	
 //make new file calculate.js
 
 const mathOperations = {
    sum: function(a,b) {
        return a + b;
    },
    
    diff: function(a,b) {
        return a - b;
    },
    product: function(a,b) {
        return a * b
    }
 }
   module.exports = mathOperations

	
 //make test file name same but test.js extension calculate.test.js
const mathOperations = require('./calculate');
describe("Calculator tests", () => {
    test('adding 1 + 2 should return 3', () => {
      expect(mathOperations.sum(1, 2)).toBe(3);
    });

    test('suntract 10 - 5 should return 5', () => {
        expect(mathOperations.diff(10,5)).toBe(5);
      });

      test("multiplying 2 and 8 should return 16", () => {
        // arrange and act
        var result = mathOperations.product(2,8)
      
        // assert
        expect(result).toBe(16);
      });
   })

	
 // to run test type npm run test