${testText}
`; // Inject HTML document.body.innerHTML = testHTML; // Add class to element and verify document.body.classList.add('foo'); // Test HTML expect(document.body.getAttribute('class')).toEqual('foo'); expect(document.body.textContent).toMatch(/Test/); expect(document.querySelectorAll('p')).toHaveLength(1); expect(document.querySelector('p').textContent).toBe(testText); expect(document.querySelector('table')).toBeNull(); }); // Snapshot Testing // https://jestjs.io/docs/en/snapshot-testing test('snapshot (jsdom)', () => { const testText = 'This is a test'; const testHTML = `${testText}
`; // Inject HTML document.body.innerHTML = testHTML; // Add class to element and verify document.body.classList.add('foo'); const documentHTML = document.documentElement.outerHTML; // Test snapshots expect(documentHTML).toMatchSnapshot(); // See __snapshots__ expect(documentHTML).toMatchInlineSnapshot( `"This is a test
"` ); }); }); describe('Fake Timers', function() { test('data & time', () => { const fakeDate = new Date().setHours(1); jest.useFakeTimers('modern'); jest.setSystemTime(fakeDate); const timeOfDay = getTimeOfDay(); expect(timeOfDay).toBe('morning'); }); }); describe('Mocks & Spys', function() { test('mock import/require dependency using jest.fn()', () => { const testModule = require('./fixtures/get-time-of-day.js'); const { greet: testGreet } = require('./fixtures/greet.js'); testModule.getTimeOfDay = jest.fn(() => 'day'); const timeOfDay = testModule.getTimeOfDay(); const greeting = testGreet('John'); expect(timeOfDay).toBe('day'); expect(greeting).toBe(`Good day, John!`); }); test('mock import/require dependency using jest.doMock()', () => { const mockModulePath = './fixtures/get-time-of-day.js'; jest.doMock(mockModulePath, () => ({ __esModule: true, getTimeOfDay: jest.fn(() => 'night'), })); const mockGetTimeOfDay = require(mockModulePath).getTimeOfDay; const { greet: testGreet } = require('./fixtures/greet.js'); const timeOfDay = mockGetTimeOfDay(); const greeting = testGreet('John'); expect(timeOfDay).toBe('night'); expect(greeting).toBe(`Good night, John!`); }); test('spy on native method using jest.spyOn()', () => { // Replace Math.random() implementation to return fixed value jest.spyOn(Math, 'random').mockImplementation(() => 0.1); expect(Math.random()).toEqual(0.1); expect(Math.random()).toEqual(0.1); expect(Math.random()).toEqual(0.1); }); test('spy on import/require dependency using jest.spyOn()', () => { jest .spyOn(getTimeOfDayModule, 'getTimeOfDay') .mockImplementation(() => 'night'); const timeOfDay = getTimeOfDay(); const greeting = greet('John'); expect(timeOfDay).toBe('night'); expect(greeting).toBe(`Good night, John!`); }); }); });