Tests Everywhere - JavaScript

class HelloMessage { text = "Hello World!"; } 

class HelloConsole { print(text) { console.log(text); } } 

class HelloApp { constructor(helloMessage, helloConsole) { this.helloMessage = helloMessage; this.helloConsole = helloConsole; } printHello() { this.helloConsole.print(this.helloMessage.text); } } 

const HelloMessage = require("./HelloMessage"); const HelloConsole = require("./HelloConsole"); const HelloApp = require("./HelloApp"); const message = new HelloMessage(); const console = new HelloConsole(); const app = new HelloApp(message, console); app.printHello(); 

describe("HelloMessage", () => { it("should return hello world", () => { const message = new HelloMessage(); expect(message.text).toBe("Hello World!"); }); }); 

// 2.1 Mock ./HelloMessage module jest.mock("./HelloMessage"); // 2.2 Mock ./HelloConsole module jest.mock("./HelloConsole"); describe("HelloApp", () => { it("should print hello message", () => { const messageText = "Hello Test!"; // 2.3 Set mock implementation to be returned // anytime new HelloMessage() is called HelloMessage.mockImplementation(() => { return { text: messageText, }; }); // 2.4 Create a HelloMessage // that will be a mock thanks to 2.1 and 2.2 const message = new HelloMessage(); // 2.5 Create a HelloConsole // that will be a mock thanks to 2.3 const console = new HelloConsole(); // 2.6 Create a HelloApp, the one we want to test, passing the mocks const app = new HelloApp(message, console); // 2.7 Execute the method we want to test app.printHello(); // 2.8 Verify HelloConsole mock print() method // has been called once with "Hello Test!" expect(console.print).toHaveBeenCalledTimes(1); expect(console.print).toHaveBeenCalledWith(messageText); }); }); 

> jest PASS ./HelloMessage.test.js PASS ./HelloApp.test.js Test Suites: 2 passed, 2 total Tests: 2 passed, 2 total Snapshots: 0 total Time: 1.229 s Ran all test suites.