test: add comprehensive unit tests for core services

Added unit tests for the `api-keys`, `auth`, `categories`, `contents`, `favorites`, `media`, and `purge` services to improve test coverage and ensure core functionality integrity.

backend/src/favorites/favorites.service.spec.ts

@@ -0,0 +1,100 @@
+import { ConflictException, NotFoundException } from "@nestjs/common";
+import { Test, TestingModule } from "@nestjs/testing";
+import { DatabaseService } from "../database/database.service";
+import { FavoritesService } from "./favorites.service";
+
+describe("FavoritesService", () => {
+	let service: FavoritesService;
+
+	const mockDb = {
+		select: jest.fn(),
+		from: jest.fn(),
+		where: jest.fn(),
+		limit: jest.fn(),
+		offset: jest.fn(),
+		innerJoin: jest.fn(),
+		insert: jest.fn(),
+		values: jest.fn(),
+		delete: jest.fn(),
+		returning: jest.fn(),
+	};
+
+	beforeEach(async () => {
+		jest.clearAllMocks();
+
+		const chain = {
+			select: jest.fn().mockReturnThis(),
+			from: jest.fn().mockReturnThis(),
+			where: jest.fn().mockReturnThis(),
+			limit: jest.fn().mockReturnThis(),
+			offset: jest.fn().mockReturnThis(),
+			innerJoin: jest.fn().mockReturnThis(),
+			insert: jest.fn().mockReturnThis(),
+			values: jest.fn().mockReturnThis(),
+			delete: jest.fn().mockReturnThis(),
+			returning: jest.fn().mockReturnThis(),
+		};
+
+		const mockImplementation = () => Object.assign(Promise.resolve([]), chain);
+		for (const mock of Object.values(chain)) {
+			mock.mockImplementation(mockImplementation);
+		}
+		Object.assign(mockDb, chain);
+
+		const module: TestingModule = await Test.createTestingModule({
+			providers: [
+				FavoritesService,
+				{ provide: DatabaseService, useValue: { db: mockDb } },
+			],
+		}).compile();
+
+		service = module.get<FavoritesService>(FavoritesService);
+	});
+
+	it("should be defined", () => {
+		expect(service).toBeDefined();
+	});
+
+	describe("addFavorite", () => {
+		it("should add a favorite", async () => {
+			mockDb.limit.mockResolvedValue([{ id: "content1" }]);
+			mockDb.returning.mockResolvedValue([
+				{ userId: "u1", contentId: "content1" },
+			]);
+
+			const result = await service.addFavorite("u1", "content1");
+
+			expect(result).toEqual([{ userId: "u1", contentId: "content1" }]);
+		});
+
+		it("should throw NotFoundException if content does not exist", async () => {
+			mockDb.limit.mockResolvedValue([]);
+			await expect(service.addFavorite("u1", "invalid")).rejects.toThrow(
+				NotFoundException,
+			);
+		});
+
+		it("should throw ConflictException on duplicate favorite", async () => {
+			mockDb.limit.mockResolvedValue([{ id: "content1" }]);
+			mockDb.returning.mockRejectedValue(new Error("Duplicate"));
+			await expect(service.addFavorite("u1", "content1")).rejects.toThrow(
+				ConflictException,
+			);
+		});
+	});
+
+	describe("removeFavorite", () => {
+		it("should remove a favorite", async () => {
+			mockDb.returning.mockResolvedValue([{ userId: "u1", contentId: "c1" }]);
+			const result = await service.removeFavorite("u1", "c1");
+			expect(result).toEqual({ userId: "u1", contentId: "c1" });
+		});
+
+		it("should throw NotFoundException if favorite not found", async () => {
+			mockDb.returning.mockResolvedValue([]);
+			await expect(service.removeFavorite("u1", "c1")).rejects.toThrow(
+				NotFoundException,
+			);
+		});
+	});
+});