test: check the sign-in callback shows the mail skeleton while it completes

app/(main)/[locale]/auth/callback/__tests__/callback-skeleton.test.tsx

@@ -0,0 +1,24 @@
+import { renderToString } from 'react-dom/server';
+import { describe, expect, it, vi } from 'vitest';
+
+// While the sign-in is completed, the callback draws the mail page's
+// skeleton: that is where it lands, and the mail page's own gate draws the
+// same, so nothing changes when it gets there.
+
+vi.mock('next/navigation', () => ({
+  useRouter: () => ({ push: vi.fn(), replace: vi.fn() }),
+  useParams: () => ({ locale: 'en' }),
+  useSearchParams: () => new URLSearchParams('code=abc&state=xyz'),
+}));
+
+const { default: OAuthCallbackPage } = await import('../page');
+
+describe('OAuth callback while the sign-in completes', () => {
+  it('server-renders the mail skeleton with the completing message, not a spinner', () => {
+    const container = document.createElement('div');
+    container.innerHTML = renderToString(<OAuthCallbackPage />);
+    expect(container.querySelector('[data-boot-skeleton="mail"]')).not.toBeNull();
+    expect(container.querySelector('[data-boot-skeleton="mail"] [role="status"]')?.textContent).toBe('oauth_completing');
+    expect(container.querySelector('.animate-spin')).toBeNull();
+  });
+});