feat(tests): add utility functions for testing with NestJS

Add test utilities to facilitate creating test apps, test users, generating tokens, and cleaning up test data in the backend codebase.

backend/test/test-utils.ts

@@ -0,0 +1,72 @@
+import { INestApplication } from '@nestjs/common';
+import { JwtService } from '@nestjs/jwt';
+import { Test, TestingModule } from '@nestjs/testing';
+import { AppModule } from '../src/app.module';
+import { UsersService } from '../src/modules/users/services/users.service';
+import { CreateUserDto } from '../src/modules/users/dto/create-user.dto';
+import { AuthService } from '../src/modules/auth/services/auth.service';
+import { ValidationPipe } from '@nestjs/common';
+import { v4 as uuidv4 } from 'uuid';
+
+/**
+ * Create a test application
+ */
+export async function createTestApp(): Promise<INestApplication> {
+  const moduleFixture: TestingModule = await Test.createTestingModule({
+    imports: [AppModule],
+  }).compile();
+
+  const app = moduleFixture.createNestApplication();
+  
+  // Apply the same middleware as in main.ts
+  app.useGlobalPipes(
+    new ValidationPipe({
+      whitelist: true,
+      transform: true,
+      forbidNonWhitelisted: true,
+    }),
+  );
+  
+  // Set global prefix as in main.ts
+  app.setGlobalPrefix('api');
+  
+  await app.init();
+  
+  return app;
+}
+
+/**
+ * Create a test user
+ */
+export async function createTestUser(app: INestApplication) {
+  const usersService = app.get(UsersService);
+  
+  const createUserDto: CreateUserDto = {
+    name: `Test User ${uuidv4().substring(0, 8)}`,
+    githubId: `github-${uuidv4().substring(0, 8)}`,
+    avatar: 'https://example.com/avatar.png',
+    metadata: { email: 'test@example.com' },
+  };
+  
+  return await usersService.create(createUserDto);
+}
+
+/**
+ * Generate JWT tokens for a user
+ */
+export async function generateTokensForUser(app: INestApplication, userId: string) {
+  const authService = app.get(AuthService);
+  return await authService.generateTokens(userId);
+}
+
+/**
+ * Clean up test data
+ */
+export async function cleanupTestData(app: INestApplication, userId: string) {
+  const usersService = app.get(UsersService);
+  try {
+    await usersService.remove(userId);
+  } catch (error) {
+    console.error(`Failed to clean up test user ${userId}:`, error.message);
+  }
+}