testdouble

import * as td from 'testdouble'; import assert from 'assert'; // Simulate a dependency module class EmailService { send(to: string, subject: string, body: string): boolean { console.log(`Sending email to ${to}: ${subject}`); return true; } } // Simulate a module under test that uses EmailService class UserService { constructor(private emailService: EmailService) {} registerUser(email: string, username: string): boolean { if (!this.emailService.send(email, 'Welcome!', `Hello ${username}, welcome!`)) { return false; } return true; } } // Test setup describe('UserService with testdouble', () => { let mockEmailService: EmailService; let userService: UserService; beforeEach(() => { // Replace the EmailService class with a test double mockEmailService = td.object<EmailService>(['send']); userService = new UserService(mockEmailService); }); afterEach(() => { td.reset(); // Clean up all test doubles after each test }); it('should register a user and send a welcome email', () => { // Stub the 'send' method to always return true td.when(mockEmailService.send('user@example.com', 'Welcome!', td.matchers.isA(String))) .thenReturn(true); const result = userService.registerUser('user@example.com', 'testuser'); assert.strictEqual(result, true); // Verify that the send method was called with expected arguments td.verify(mockEmailService.send('user@example.com', 'Welcome!', 'Hello testuser, welcome!'), { times: 1 }); }); it('should handle email sending failure', () => { // Stub the 'send' method to return false td.when(mockEmailService.send(td.matchers.anything(), td.matchers.anything(), td.matchers.anything())) .thenReturn(false); const result = userService.registerUser('fail@example.com', 'failuser'); assert.strictEqual(result, false); td.verify(mockEmailService.send(td.matchers.anything(), td.matchers.anything(), td.matchers.anything()), { times: 1 }); }); });