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..8a7311f
--- /dev/null
+++ b/src/app/api/dashboard/summary/route.test.ts
@@ -0,0 +1,138 @@
+import { describe, expect, it, vi, beforeEach } from "vitest";
+import { getServerSession } from "next-auth";
+import { fetchUserSummary } from "@/lib/github";
+import { fetchViewerLogin } from "@/lib/githubViewer";
+
+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.clearAllMocks();
+  });
+
+  it("returns 401 if no session exists", async () => {
+    vi.mocked(getServerSession).mockResolvedValueOnce(null);
+
+    const { GET } = await import("./route");
+    const response = await GET();
+    const data = await response.json();
+
+    expect(response.status).toBe(401);
+    expect(data.error).toBe("Unauthorized");
+  });
+
+  it("returns 401 if no access token exists", async () => {
+    vi.mocked(getServerSession).mockResolvedValueOnce({ user: { login: "testuser" } });
+
+    const { GET } = await import("./route");
+    const response = await GET();
+    const data = await response.json();
+
+    expect(response.status).toBe(401);
+    expect(data.error).toBe("Unauthorized");
+  });
+
+  it("returns 200 and summary if session has login", async () => {
+    const mockSession = {
+      accessToken: "fake-token",
+      user: { login: "testuser" },
+    };
+    const mockSummary = { profile: { login: "testuser" } };
+
+    vi.mocked(getServerSession).mockResolvedValueOnce(mockSession);
+    vi.mocked(fetchUserSummary).mockResolvedValueOnce(mockSummary as any);
+
+    const { GET } = await import("./route");
+    const response = await GET();
+    const data = await response.json();
+
+    expect(response.status).toBe(200);
+    expect(data.username).toBe("testuser");
+    expect(data.summary).toEqual(mockSummary);
+    expect(fetchViewerLogin).not.toHaveBeenCalled();
+    expect(fetchUserSummary).toHaveBeenCalledWith("testuser", "fake-token");
+  });
+
+  it("returns 200 and fetches login if missing from session", async () => {
+    const mockSession = {
+      accessToken: "fake-token",
+      user: { name: "Test User" }, // login missing
+    };
+    const mockSummary = { profile: { login: "testuser" } };
+
+    vi.mocked(getServerSession).mockResolvedValueOnce(mockSession);
+    vi.mocked(fetchViewerLogin).mockResolvedValueOnce("testuser");
+    vi.mocked(fetchUserSummary).mockResolvedValueOnce(mockSummary as any);
+
+    const { GET } = await import("./route");
+    const response = await GET();
+    const data = await response.json();
+
+    expect(response.status).toBe(200);
+    expect(data.username).toBe("testuser");
+    expect(data.summary).toEqual(mockSummary);
+    expect(fetchViewerLogin).toHaveBeenCalledWith("fake-token");
+    expect(fetchUserSummary).toHaveBeenCalledWith("testuser", "fake-token");
+  });
+
+  it("returns 500 if fetchViewerLogin fails", async () => {
+    const mockSession = {
+      accessToken: "fake-token",
+      user: { name: "Test User" }, // login missing
+    };
+
+    vi.mocked(getServerSession).mockResolvedValueOnce(mockSession);
+    vi.mocked(fetchViewerLogin).mockRejectedValueOnce(new Error("Viewer login failed"));
+
+    const { GET } = await import("./route");
+    const response = await GET();
+    const data = await response.json();
+
+    expect(response.status).toBe(500);
+    expect(data.error).toBe("Viewer login failed");
+  });
+
+  it("returns 500 if fetchUserSummary fails", async () => {
+    const mockSession = {
+      accessToken: "fake-token",
+      user: { login: "testuser" },
+    };
+
+    vi.mocked(getServerSession).mockResolvedValueOnce(mockSession);
+    vi.mocked(fetchUserSummary).mockRejectedValueOnce(new Error("Summary fetch failed"));
+
+    const { GET } = await import("./route");
+    const response = await GET();
+    const data = await response.json();
+
+    expect(response.status).toBe(500);
+    expect(data.error).toBe("Summary fetch failed");
+  });
+
+  it("returns 500 with 'Unknown error' if error is not an Error instance", async () => {
+    const mockSession = {
+      accessToken: "fake-token",
+      user: { login: "testuser" },
+    };
+
+    vi.mocked(getServerSession).mockResolvedValueOnce(mockSession);
+    vi.mocked(fetchUserSummary).mockRejectedValueOnce("Something went wrong");
+
+    const { GET } = await import("./route");
+    const response = await GET();
+    const data = await response.json();
+
+    expect(response.status).toBe(500);
+    expect(data.error).toBe("Unknown error");
+  });
+});