add unit tests

tests/setup.ts

@@ -0,0 +1,15 @@
+// Required by React to silence act(...) warnings in jsdom tests.
+globalThis.IS_REACT_ACT_ENVIRONMENT = true;
+
+import '@testing-library/jest-dom/vitest';
+import { cleanup } from '@testing-library/react';
+import { afterEach, vi } from 'vitest';
+
+vi.mock('@mdxeditor/editor', () => import('./mocks/mdxeditor'));
+
+afterEach(() => {
+    cleanup();
+    localStorage.clear();
+    vi.restoreAllMocks();
+    vi.useRealTimers();
+});