diff --git a/src/app/api/dashboard/summary/route.test.ts b/src/app/api/dashboard/summary/route.test.ts
new file mode 100644
index 0000000..16d3b16
--- /dev/null
+++ b/src/app/api/dashboard/summary/route.test.ts
@@ -0,0 +1,120 @@
+import { describe, expect, it, vi, beforeEach } from "vitest";
+import { GET } from "./route";
+
+import type { Session } from "next-auth";
+
+vi.mock("next-auth", () => ({
+    getServerSession: vi.fn(),
+}));
+
+vi.mock("@/lib/github", () => ({
+    fetchUserSummary: vi.fn(),
+}));
+
+vi.mock("@/lib/githubViewer", () => ({
+    fetchViewerLogin: vi.fn(),
+}));
+
+describe("GET /api/dashboard/summary", () => {
+    beforeEach(() => {
+        vi.resetAllMocks();
+    });
+
+    it("returns 401 if unauthorized", async () => {
+        const { getServerSession } = await import("next-auth");
+        vi.mocked(getServerSession).mockResolvedValueOnce(null);
+
+        const response = await GET();
+        const data = await response.json();
+
+        expect(response.status).toBe(401);
+        expect(data).toEqual({ error: "Unauthorized" });
+    });
+
+    it("returns summary if session contains user login", async () => {
+        const { getServerSession } = await import("next-auth");
+        const { fetchUserSummary } = await import("@/lib/github");
+
+        vi.mocked(getServerSession).mockResolvedValueOnce({
+            user: { login: "testuser" },
+            accessToken: "token123",
+        } as unknown as Session);
+
+        vi.mocked(fetchUserSummary).mockResolvedValueOnce({
+            text: "This is a summary",
+        } as unknown as import('@/lib/types').UserSummary);
+
+        const response = await GET();
+        const data = await response.json();
+
+        expect(response.status).toBe(200);
+        expect(data).toEqual({
+            username: "testuser",
+            summary: { text: "This is a summary" },
+        });
+        expect(fetchUserSummary).toHaveBeenCalledWith("testuser", "token123");
+    });
+
+    it("returns summary using fetchViewerLogin if session user login is missing", async () => {
+        const { getServerSession } = await import("next-auth");
+        const { fetchUserSummary } = await import("@/lib/github");
+        const { fetchViewerLogin } = await import("@/lib/githubViewer");
+
+        vi.mocked(getServerSession).mockResolvedValueOnce({
+            accessToken: "token123",
+        } as unknown as Session);
+
+        vi.mocked(fetchViewerLogin).mockResolvedValueOnce("viewerlogin");
+
+        vi.mocked(fetchUserSummary).mockResolvedValueOnce({
+            text: "Viewer summary",
+        } as unknown as import('@/lib/types').UserSummary);
+
+        const response = await GET();
+        const data = await response.json();
+
+        expect(response.status).toBe(200);
+        expect(data).toEqual({
+            username: "viewerlogin",
+            summary: { text: "Viewer summary" },
+        });
+        expect(fetchViewerLogin).toHaveBeenCalledWith("token123");
+        expect(fetchUserSummary).toHaveBeenCalledWith("viewerlogin", "token123");
+    });
+
+    it("returns 500 if fetchUserSummary throws an Error", async () => {
+        const { getServerSession } = await import("next-auth");
+        const { fetchUserSummary } = await import("@/lib/github");
+
+        vi.mocked(getServerSession).mockResolvedValueOnce({
+            user: { login: "erroruser" },
+            accessToken: "token123",
+        } as unknown as Session);
+
+        vi.mocked(fetchUserSummary).mockRejectedValueOnce(new Error("API Error"));
+
+        const response = await GET();
+        const data = await response.json();
+
+        expect(response.status).toBe(500);
+        expect(data).toEqual({ error: "API Error" });
+    });
+
+    it("returns 500 if fetchUserSummary throws a non-Error", async () => {
+        const { getServerSession } = await import("next-auth");
+        const { fetchUserSummary } = await import("@/lib/github");
+
+        vi.mocked(getServerSession).mockResolvedValueOnce({
+            user: { login: "erroruser" },
+            accessToken: "token123",
+        } as unknown as Session);
+
+        vi.mocked(fetchUserSummary).mockRejectedValueOnce("String error");
+
+        const response = await GET();
+        const data = await response.json();
+
+        expect(response.status).toBe(500);
+        expect(data).toEqual({ error: "Unknown error" });
+    });
+});