Set up PostgreSQL database configuration and enhance application structure

- Added .env.example with database connection details and JWT configuration.
- Introduced docker-compose.yml for PostgreSQL service setup with health checks.
- Created drizzle.config.ts for database schema and migration management.
- Updated nest-cli.json to include Swagger plugin configuration for API documentation.
- Enhanced package.json with new database-related scripts and dependencies.
- Implemented initial database migrations for user and token management.
- Configured application bootstrap process to load environment variables and set up Swagger.
- Added shared application configuration in configure-app.ts for consistent setup.
- Included unit tests for application configuration and Swagger setup.

src/modules/users/users.service.spec.ts

@@ -0,0 +1,71 @@
+import { ConflictException } from '@nestjs/common';
+import { Test, TestingModule } from '@nestjs/testing';
+import { DateTime } from '../../common/value-objects/date-time/date-time';
+import type { User } from './user';
+import { UsersRepository } from './users.repository';
+import { UsersService } from './users.service';
+
+describe('UsersService', () => {
+  let service: UsersService;
+  let repository: jest.Mocked<
+    Pick<UsersRepository, 'findById' | 'findByUsername' | 'create'>
+  >;
+
+  const now = DateTime.fromUnixMs(1_700_000_000_000);
+  const sampleUser: User = {
+    id: 'user-1',
+    username: 'alice',
+    passwordHash: 'hashed',
+    createdAt: now,
+    updatedAt: now,
+  };
+
+  beforeEach(async () => {
+    repository = {
+      findById: jest.fn(),
+      findByUsername: jest.fn(),
+      create: jest.fn(),
+    };
+
+    const moduleRef: TestingModule = await Test.createTestingModule({
+      providers: [
+        UsersService,
+        { provide: UsersRepository, useValue: repository },
+      ],
+    }).compile();
+
+    service = moduleRef.get(UsersService);
+  });
+
+  it('findById delegates to repository', async () => {
+    repository.findById.mockResolvedValue(sampleUser);
+    await expect(service.findById('user-1')).resolves.toEqual(sampleUser);
+  });
+
+  it('create stores lowercase username', async () => {
+    repository.findByUsername.mockResolvedValue(null);
+    repository.create.mockResolvedValue(sampleUser);
+
+    await service.create('Alice', 'hashed');
+
+    expect(repository.findByUsername).toHaveBeenCalledWith('alice');
+    expect(repository.create).toHaveBeenCalledWith({
+      username: 'alice',
+      passwordHash: 'hashed',
+    });
+  });
+
+  it('create throws ConflictException when username exists', async () => {
+    repository.findByUsername.mockResolvedValue(sampleUser);
+
+    await expect(service.create('alice', 'hashed')).rejects.toBeInstanceOf(
+      ConflictException,
+    );
+    expect(repository.create).not.toHaveBeenCalled();
+  });
+
+  it('findByUsername delegates to repository', async () => {
+    repository.findByUsername.mockResolvedValue(sampleUser);
+    await expect(service.findByUsername('Alice')).resolves.toEqual(sampleUser);
+  });
+});