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/common/services/purge.service.spec.ts

@@ -0,0 +1,67 @@
+import { Logger } from "@nestjs/common";
+import { Test, TestingModule } from "@nestjs/testing";
+import { DatabaseService } from "../../database/database.service";
+import { PurgeService } from "./purge.service";
+
+describe("PurgeService", () => {
+	let service: PurgeService;
+
+	const mockDb = {
+		delete: jest.fn(),
+		where: jest.fn(),
+		returning: jest.fn(),
+	};
+
+	beforeEach(async () => {
+		jest.clearAllMocks();
+		jest.spyOn(Logger.prototype, "error").mockImplementation(() => {});
+		jest.spyOn(Logger.prototype, "log").mockImplementation(() => {});
+
+		const chain = {
+			delete: jest.fn().mockReturnThis(),
+			where: jest.fn().mockReturnThis(),
+			returning: jest.fn().mockResolvedValue([]),
+		};
+
+		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: [
+				PurgeService,
+				{ provide: DatabaseService, useValue: { db: mockDb } },
+			],
+		}).compile();
+
+		service = module.get<PurgeService>(PurgeService);
+	});
+
+	it("should be defined", () => {
+		expect(service).toBeDefined();
+	});
+
+	describe("purgeExpiredData", () => {
+		it("should purge data", async () => {
+			mockDb.returning
+				.mockResolvedValueOnce([{ id: "s1" }]) // sessions
+				.mockResolvedValueOnce([{ id: "r1" }]) // reports
+				.mockResolvedValueOnce([{ id: "u1" }]) // users
+				.mockResolvedValueOnce([{ id: "c1" }]); // contents
+
+			await service.purgeExpiredData();
+
+			expect(mockDb.delete).toHaveBeenCalledTimes(4);
+			expect(mockDb.returning).toHaveBeenCalledTimes(4);
+		});
+
+		it("should handle errors", async () => {
+			mockDb.delete.mockImplementation(() => {
+				throw new Error("Db error");
+			});
+			await expect(service.purgeExpiredData()).resolves.not.toThrow();
+		});
+	});
+});