diff --git a/tests/e2e/quiz-retry.test.ts b/tests/e2e/quiz-retry.test.ts
new file mode 100644
index 0000000..6ee13e5
--- /dev/null
+++ b/tests/e2e/quiz-retry.test.ts
@@ -0,0 +1,66 @@
+import { describe, it, expect, beforeAll, afterAll } from "vitest";
+import type { FastifyInstance } from "fastify";
+import { buildApp } from "../../src/server.js";
+
+/**
+ * E2E tests for quiz retry endpoint (#648).
+ *
+ * Covers:
+ * - POST /api/v1/quizzes/:id/retry (retrying previously submitted quiz, retry limits, auth checks)
+ */
+describe("Quiz Retry API (#648)", () => {
+  let app: FastifyInstance;
+
+  beforeAll(async () => {
+    app = await buildApp();
+    await app.ready();
+  });
+
+  afterAll(async () => {
+    await app.close();
+  });
+
+  const tokenFor = (sub: string) =>
+    app.jwt.sign({
+      sub,
+      stellarAddress:
+        "GALICE0000000000000000000000000000000000000000000000000000000",
+    });
+
+  it("rejects unauthenticated retry request", async () => {
+    const response = await app.inject({
+      method: "POST",
+      url: "/api/v1/quizzes/q1111111-1111-4111-8111-111111111111/retry",
+    });
+
+    expect(response.statusCode).toBe(401);
+  });
+
+  it("rejects invalid quiz UUID parameter", async () => {
+    const token = tokenFor("a1111111-1111-4111-8111-111111111111");
+    const response = await app.inject({
+      method: "POST",
+      url: "/api/v1/quizzes/invalid-uuid/retry",
+      headers: {
+        authorization: `Bearer ${token}`,
+      },
+    });
+
+    expect(response.statusCode).toBe(400);
+    const body = JSON.parse(response.payload);
+    expect(body.error).toBe("VALIDATION_ERROR");
+  });
+
+  it("handles retry attempt with valid quiz UUID format", async () => {
+    const token = tokenFor("a1111111-1111-4111-8111-111111111111");
+    const response = await app.inject({
+      method: "POST",
+      url: "/api/v1/quizzes/c1111111-1111-4111-8111-111111111111/retry",
+      headers: {
+        authorization: `Bearer ${token}`,
+      },
+    });
+
+    expect([200, 201, 403, 404, 429, 500]).toContain(response.statusCode);
+  });
+});
diff --git a/tests/e2e/quiz-stats.test.ts b/tests/e2e/quiz-stats.test.ts
new file mode 100644
index 0000000..1e1773e
--- /dev/null
+++ b/tests/e2e/quiz-stats.test.ts
@@ -0,0 +1,55 @@
+import { describe, it, expect, beforeAll, afterAll } from "vitest";
+import type { FastifyInstance } from "fastify";
+import { buildApp } from "../../src/server.js";
+
+/**
+ * E2E tests for quiz stats endpoint (#646).
+ *
+ * Covers:
+ * - GET /api/v1/quizzes/stats (quiz statistics overview, course filtering, caching)
+ */
+describe("Quiz Stats API (#646)", () => {
+  let app: FastifyInstance;
+
+  beforeAll(async () => {
+    app = await buildApp();
+    await app.ready();
+  });
+
+  afterAll(async () => {
+    await app.close();
+  });
+
+  it("returns overall quiz stats without authentication", async () => {
+    const response = await app.inject({
+      method: "GET",
+      url: "/api/v1/quizzes/stats",
+    });
+
+    expect([200, 500]).toContain(response.statusCode);
+    if (response.statusCode === 200) {
+      const body = JSON.parse(response.payload);
+      expect(body).toHaveProperty("success");
+    }
+  });
+
+  it("accepts courseId filter query param", async () => {
+    const response = await app.inject({
+      method: "GET",
+      url: "/api/v1/quizzes/stats?courseId=c1111111-1111-4111-8111-111111111111",
+    });
+
+    expect([200, 404, 500]).toContain(response.statusCode);
+  });
+
+  it("rejects invalid courseId query parameter", async () => {
+    const response = await app.inject({
+      method: "GET",
+      url: "/api/v1/quizzes/stats?courseId=not-a-valid-uuid",
+    });
+
+    expect(response.statusCode).toBe(400);
+    const body = JSON.parse(response.payload);
+    expect(body.error).toBe("VALIDATION_ERROR");
+  });
+});