test(api): add unit and integration tests for game service and endpoints

- Unit tests for createGameSession and evaluateAnswer (14 tests)
- Endpoint tests for POST /game/start and /game/answer via supertest (8 tests)
- Mock @glossa/db — no real database dependency

apps/api/src/controllers/gameController.test.ts

@@ -0,0 +1,139 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import request from "supertest";
+
+vi.mock("@glossa/db", () => ({
+  getGameTerms: vi.fn(),
+  getDistractors: vi.fn(),
+}));
+
+import { getGameTerms, getDistractors } from "@glossa/db";
+import { createApp } from "../app.js";
+
+const app = createApp();
+const mockGetGameTerms = vi.mocked(getGameTerms);
+const mockGetDistractors = vi.mocked(getDistractors);
+
+const validBody = {
+  source_language: "en",
+  target_language: "it",
+  pos: "noun",
+  difficulty: "easy",
+  rounds: "3",
+};
+
+const fakeTerms = [
+  { termId: "t1", sourceText: "dog", targetText: "cane", sourceGloss: null },
+  { termId: "t2", sourceText: "cat", targetText: "gatto", sourceGloss: null },
+  { termId: "t3", sourceText: "house", targetText: "casa", sourceGloss: null },
+];
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  mockGetGameTerms.mockResolvedValue(fakeTerms);
+  mockGetDistractors.mockResolvedValue(["wrong1", "wrong2", "wrong3"]);
+});
+
+describe("POST /api/v1/game/start", () => {
+  it("returns 200 with a valid game session", async () => {
+    const res = await request(app).post("/api/v1/game/start").send(validBody);
+
+    expect(res.status).toBe(200);
+    expect(res.body.success).toBe(true);
+    expect(res.body.data.sessionId).toBeDefined();
+    expect(res.body.data.questions).toHaveLength(3);
+  });
+
+  it("returns 400 when the body is empty", async () => {
+    const res = await request(app).post("/api/v1/game/start").send({});
+
+    expect(res.status).toBe(400);
+    expect(res.body.success).toBe(false);
+    expect(res.body.error).toBeDefined();
+  });
+
+  it("returns 400 when required fields are missing", async () => {
+    const res = await request(app)
+      .post("/api/v1/game/start")
+      .send({ source_language: "en" });
+
+    expect(res.status).toBe(400);
+    expect(res.body.success).toBe(false);
+  });
+
+  it("returns 400 when a field has an invalid value", async () => {
+    const res = await request(app)
+      .post("/api/v1/game/start")
+      .send({ ...validBody, difficulty: "impossible" });
+
+    expect(res.status).toBe(400);
+    expect(res.body.success).toBe(false);
+  });
+});
+
+describe("POST /api/v1/game/answer", () => {
+  it("returns 200 with an answer result for a valid submission", async () => {
+    // Start a game first
+    const startRes = await request(app)
+      .post("/api/v1/game/start")
+      .send(validBody);
+
+    const { sessionId, questions } = startRes.body.data;
+    const question = questions[0];
+
+    const res = await request(app)
+      .post("/api/v1/game/answer")
+      .send({
+        sessionId,
+        questionId: question.questionId,
+        selectedOptionId: 0,
+      });
+
+    expect(res.status).toBe(200);
+    expect(res.body.success).toBe(true);
+    expect(res.body.data.questionId).toBe(question.questionId);
+    expect(typeof res.body.data.isCorrect).toBe("boolean");
+    expect(typeof res.body.data.correctOptionId).toBe("number");
+    expect(res.body.data.selectedOptionId).toBe(0);
+  });
+
+  it("returns 400 when the body is empty", async () => {
+    const res = await request(app).post("/api/v1/game/answer").send({});
+
+    expect(res.status).toBe(400);
+    expect(res.body.success).toBe(false);
+  });
+
+  it("returns 404 when the session does not exist", async () => {
+    const res = await request(app)
+      .post("/api/v1/game/answer")
+      .send({
+        sessionId: "00000000-0000-0000-0000-000000000000",
+        questionId: "00000000-0000-0000-0000-000000000000",
+        selectedOptionId: 0,
+      });
+
+    expect(res.status).toBe(404);
+    expect(res.body.success).toBe(false);
+    expect(res.body.error).toContain("Game session not found");
+  });
+
+  it("returns 404 when the question does not exist in the session", async () => {
+    const startRes = await request(app)
+      .post("/api/v1/game/start")
+      .send(validBody);
+
+    const { sessionId } = startRes.body.data;
+
+    const res = await request(app)
+      .post("/api/v1/game/answer")
+      .send({
+        sessionId,
+        questionId: "00000000-0000-0000-0000-000000000000",
+        selectedOptionId: 0,
+      });
+
+    expect(res.status).toBe(404);
+    expect(res.body.success).toBe(false);
+    expect(res.body.error).toContain("Question not found");
+  });
+});