test(auth): add unit tests for various guards and services with mocked dependencies

backend/src/database/database.service.spec.ts

@@ -0,0 +1,67 @@
+import { ConfigService } from "@nestjs/config";
+import { Test, TestingModule } from "@nestjs/testing";
+import { DatabaseService } from "./database.service";
+
+jest.mock("pg", () => {
+	const mPool = {
+		connect: jest.fn(),
+		query: jest.fn(),
+		end: jest.fn(),
+		on: jest.fn(),
+	};
+	return { Pool: jest.fn(() => mPool) };
+});
+
+jest.mock("drizzle-orm/node-postgres", () => ({
+	drizzle: jest.fn().mockReturnValue({}),
+}));
+
+describe("DatabaseService", () => {
+	let service: DatabaseService;
+	let _configService: ConfigService;
+
+	const mockConfigService = {
+		get: jest.fn((key) => {
+			const config = {
+				POSTGRES_PASSWORD: "p",
+				POSTGRES_USER: "u",
+				POSTGRES_HOST: "h",
+				POSTGRES_PORT: "5432",
+				POSTGRES_DB: "db",
+				NODE_ENV: "development",
+			};
+			return config[key];
+		}),
+	};
+
+	beforeEach(async () => {
+		const module: TestingModule = await Test.createTestingModule({
+			providers: [
+				DatabaseService,
+				{ provide: ConfigService, useValue: mockConfigService },
+			],
+		}).compile();
+
+		service = module.get<DatabaseService>(DatabaseService);
+		_configService = module.get<ConfigService>(ConfigService);
+	});
+
+	it("should be defined", () => {
+		expect(service).toBeDefined();
+	});
+
+	describe("onModuleInit", () => {
+		it("should skip migrations in development", async () => {
+			await service.onModuleInit();
+			expect(mockConfigService.get).toHaveBeenCalledWith("NODE_ENV");
+		});
+	});
+
+	describe("onModuleDestroy", () => {
+		it("should close pool", async () => {
+			const pool = (service as any).pool;
+			await service.onModuleDestroy();
+			expect(pool.end).toHaveBeenCalled();
+		});
+	});
+});