test(not-found): add massive scaling coverage for repeated renders and layout stability

app/not-found.massive-scaling.test.tsx

@@ -0,0 +1,86 @@
+import { describe, expect, it, vi } from 'vitest';
+import { cleanup, render, screen } from '@testing-library/react';
+import NotFound from './not-found';
+
+vi.mock('next/link', () => ({
+  default: ({ href, children, ...props }: { href: string; children: React.ReactNode }) => (
+    <a href={href} {...props}>
+      {children}
+    </a>
+  ),
+}));
+
+vi.mock('sonner', () => ({
+  toast: {
+    success: vi.fn(),
+    error: vi.fn(),
+  },
+}));
+
+describe('NotFound — massive scaling', () => {
+  it('renders successfully across many repeated mounts', () => {
+    for (let i = 0; i < 250; i++) {
+      const { unmount } = render(<NotFound />);
+      expect(screen.getAllByText('𝒐𝒐𝒑𝒔').length).toBe(2);
+      unmount();
+    }
+  });
+
+  it('maintains terminal content integrity during repeated renders', () => {
+    for (let i = 0; i < 100; i++) {
+      render(<NotFound />);
+
+      expect(screen.getByText(/The page you're looking for has been rebased/i)).toBeInTheDocument();
+
+      cleanup();
+    }
+  });
+
+  it('keeps navigation links available under high render volume', () => {
+    render(
+      <>
+        {Array.from({ length: 50 }).map((_, index) => (
+          <div key={index}>
+            <NotFound />
+          </div>
+        ))}
+      </>
+    );
+
+    expect(screen.getAllByRole('link', { name: /go back home/i })).toHaveLength(50);
+
+    expect(screen.getAllByRole('link', { name: /git checkout main/i })).toHaveLength(50);
+  });
+
+  it('renders within acceptable performance limits', () => {
+    const start = performance.now();
+
+    for (let i = 0; i < 100; i++) {
+      const { unmount } = render(<NotFound />);
+      unmount();
+    }
+
+    const duration = performance.now() - start;
+
+    expect(duration).toBeLessThan(5000);
+  });
+
+  it('preserves layout structure under bulk rendering conditions', () => {
+    const { container } = render(
+      <>
+        {Array.from({ length: 25 }).map((_, index) => (
+          <NotFound key={index} />
+        ))}
+      </>
+    );
+
+    const mainElements = container.querySelectorAll('main');
+
+    expect(mainElements.length).toBe(25);
+
+    mainElements.forEach((element) => {
+      expect(element.className).toContain('min-h-screen');
+      expect(element.className).toContain('flex');
+    });
+  });
+});