diff --git a/app/components/UserList.test.tsx b/app/components/UserList.test.tsx
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+++ b/app/components/UserList.test.tsx
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+/**
+ * Tests for app/components/UserList.tsx ("Bad" version from PR).
+ *
+ * Detected/Assumed framework: Jest + @testing-library/react + jsdom
+ * - If the repo uses Vitest, replace jest-specific globals with vitest equivalents.
+ *
+ * Scenarios:
+ *  - Renders list on happy path and lowercases emails
+ *  - Renders "No users found." on empty array
+ *  - Still renders when HTTP status is non-ok (since code doesn't check response.ok)
+ *  - Throws when a user's email is null/undefined (due to .toLowerCase())
+ *  - Logs React key warning due to missing `key` on list items
+ *  - Uses <a href="/profile"> (internal link) for each user
+ */
+
+import React from "react";
+import { render, screen, within } from "@testing-library/react";
+
+jest.mock("next/link", () => {
+  // Not used by the bad component, but in case Next Link gets auto-mocked elsewhere.
+  return ({ children }: any) => children;
+});
+
+describe("UserList (bad PR version)", () => {
+  const origFetch = global.fetch as any;
+  const origError = console.error;
+
+  beforeEach(() => {
+    // jsdom environment expected
+    jest.resetModules();
+    jest.clearAllMocks();
+    // Default fetch mock returns two users
+    global.fetch = jest.fn().mockResolvedValue({
+      ok: true,
+      status: 200,
+      json: async () => ([
+        { id: 1, name: "Alice", email: "ALICE@EXAMPLE.COM" },
+        { id: 2, name: "Bob", email: "Bob@Example.Com" },
+      ]),
+    }) as any;
+    // Silence React act/key warnings per-test unless explicitly asserted
+    console.error = jest.fn();
+  });
+
+  afterEach(() => {
+    global.fetch = origFetch;
+    console.error = origError;
+  });
+
+  async function loadComponent() {
+    // Import inside to pick up fresh mocks after jest.resetModules
+    const mod = await import("./UserList"); // Prefer app/components/UserList.tsx
+    // The default export is an async function returning JSX
+    // We call it to obtain the React element.
+    const element = await (mod.default as any)();
+    return element;
+  }
+
+  test("renders the title and user items (happy path) and lowercases emails", async () => {
+    const element = await loadComponent();
+    render(element);
+
+    // Title
+    expect(screen.getByRole("heading", { level: 1, name: "User List" })).toBeInTheDocument();
+
+    // List and items
+    const list = screen.getByRole("list");
+    const items = within(list).getAllByRole("listitem");
+    expect(items).toHaveLength(2);
+
+    // Names
+    expect(within(items[0]).getByText("Alice")).toBeInTheDocument();
+    expect(within(items[1]).getByText("Bob")).toBeInTheDocument();
+
+    // Emails are lowercased by the implementation
+    expect(within(items[0]).getByText("alice@example.com")).toBeInTheDocument();
+    expect(within(items[1]).getByText("bob@example.com")).toBeInTheDocument();
+
+    // Each item includes an internal anchor link to "/profile"
+    const anchors = screen.getAllByRole("link", { name: "View Profile" });
+    expect(anchors).toHaveLength(2);
+    anchors.forEach(a => {
+      expect(a).toHaveAttribute("href", "/profile");
+    });
+  });
+
+  test('renders "No users found." when API returns empty array', async () => {
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      status: 200,
+      json: async () => ([]),
+    });
+
+    const element = await loadComponent();
+    render(element);
+
+    expect(screen.getByText("No users found.")).toBeInTheDocument();
+  });
+
+  test("still renders list even when HTTP status is non-ok (no ok check in code)", async () => {
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: false,
+      status: 500,
+      json: async () => ([
+        { id: 7, name: "Carol", email: "Carol@Example.com" },
+      ]),
+    });
+
+    const element = await loadComponent();
+    render(element);
+
+    // Despite status 500, the component uses response.json() and renders
+    const items = screen.getAllByRole("listitem");
+    expect(items).toHaveLength(1);
+    expect(screen.getByText("carol@example.com")).toBeInTheDocument();
+  });
+
+  test("throws when a user's email is null (due to .toLowerCase() without a guard)", async () => {
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      status: 200,
+      json: async () => ([
+        { id: 1, name: "Null Email", email: null },
+      ]),
+    });
+
+    await expect(loadComponent()).rejects.toThrow();
+  });
+
+  test("emits React key warning due to missing `key` on list items", async () => {
+    // Arrange: keep two users to trigger map without keys
+    const element = await loadComponent();
+    render(element);
+
+    // React warns to console.error about missing keys.
+    // We check that console.error was called with the key warning substring.
+    // Note: The exact message can vary by React version; match on core phrase.
+    const errorCalls = (console.error as jest.Mock).mock.calls
+      .flat()
+      .map(String)
+      .join("\n");
+    expect(errorCalls).toMatch(/unique "key" prop|unique key/i);
+  });
+
+  test('displays "No users found." when API returns non-array JSON (e.g., error object)', async () => {
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: false,
+      status: 500,
+      json: async () => ({ error: "Internal error" }),
+    });
+
+    const element = await loadComponent();
+    render(element);
+
+    expect(screen.getByText("No users found.")).toBeInTheDocument();
+  });
+
+  test("propagates fetch rejection (no error handling in getUsers)", async () => {
+    (global.fetch as jest.Mock).mockRejectedValueOnce(new Error("network down"));
+
+    await expect(loadComponent()).rejects.toThrow(/network down/i);
+  });
+});
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