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/users/users.service.spec.ts

@@ -0,0 +1,114 @@
+jest.mock("@noble/post-quantum/ml-kem.js", () => ({
+	ml_kem768: {
+		keygen: jest.fn(),
+		encapsulate: jest.fn(),
+		decapsulate: jest.fn(),
+	},
+}));
+
+jest.mock("jose", () => ({
+	SignJWT: jest.fn(),
+	jwtVerify: jest.fn(),
+}));
+
+import { Test, TestingModule } from "@nestjs/testing";
+import { CryptoService } from "../crypto/crypto.service";
+import { DatabaseService } from "../database/database.service";
+import { UsersService } from "./users.service";
+
+describe("UsersService", () => {
+	let service: UsersService;
+
+	const mockDb = {
+		insert: jest.fn(),
+		select: jest.fn(),
+		update: jest.fn(),
+		transaction: jest.fn().mockImplementation((cb) => cb(mockDb)),
+	};
+
+	const mockCryptoService = {
+		getPgpEncryptionKey: jest.fn().mockReturnValue("mock-pgp-key"),
+	};
+
+	beforeEach(async () => {
+		jest.clearAllMocks();
+
+		const chain = {
+			insert: jest.fn().mockReturnThis(),
+			values: jest.fn().mockReturnThis(),
+			returning: jest.fn().mockReturnThis(),
+			select: jest.fn().mockReturnThis(),
+			from: jest.fn().mockReturnThis(),
+			where: jest.fn().mockReturnThis(),
+			limit: jest.fn().mockReturnThis(),
+			offset: jest.fn().mockReturnThis(),
+			update: jest.fn().mockReturnThis(),
+			set: jest.fn().mockReturnThis(),
+			// biome-ignore lint/suspicious/noThenProperty: Fine for testing purposes
+			then: jest.fn().mockImplementation(function (cb) {
+				return Promise.resolve(this).then(cb);
+			}),
+		};
+
+		const mockImplementation = () => Object.assign(Promise.resolve([]), chain);
+		for (const mock of Object.values(chain)) {
+			if (mock !== chain.then) {
+				mock.mockImplementation(mockImplementation);
+			}
+		}
+		Object.assign(mockDb, chain);
+
+		const module: TestingModule = await Test.createTestingModule({
+			providers: [
+				UsersService,
+				{ provide: DatabaseService, useValue: { db: mockDb } },
+				{ provide: CryptoService, useValue: mockCryptoService },
+			],
+		}).compile();
+
+		service = module.get<UsersService>(UsersService);
+	});
+
+	it("should be defined", () => {
+		expect(service).toBeDefined();
+	});
+
+	describe("create", () => {
+		it("should create a user", async () => {
+			const data = {
+				username: "u1",
+				email: "e1",
+				passwordHash: "p1",
+				emailHash: "eh1",
+			};
+			mockDb.returning.mockResolvedValue([{ uuid: "uuid1", ...data }]);
+
+			const result = await service.create(data);
+
+			expect(result.uuid).toBe("uuid1");
+			expect(mockDb.insert).toHaveBeenCalled();
+		});
+	});
+
+	describe("findOne", () => {
+		it("should find a user", async () => {
+			mockDb.limit.mockResolvedValue([{ uuid: "uuid1" }]);
+			const result = await service.findOne("uuid1");
+			expect(result.uuid).toBe("uuid1");
+		});
+
+		it("should return null if not found", async () => {
+			mockDb.limit.mockResolvedValue([]);
+			const result = await service.findOne("uuid1");
+			expect(result).toBeNull();
+		});
+	});
+
+	describe("update", () => {
+		it("should update a user", async () => {
+			mockDb.returning.mockResolvedValue([{ uuid: "uuid1", displayName: "New" }]);
+			const result = await service.update("uuid1", { displayName: "New" });
+			expect(result[0].displayName).toBe("New");
+		});
+	});
+});