fix Quick Start Page Heading Order (#8594)

src/components/MDX/SimpleCallout.tsx

@@ -11,7 +11,7 @@
 
 import * as React from 'react';
 import cn from 'classnames';
-import {H3} from './Heading';
+import {H2} from './Heading';
 
 interface SimpleCalloutProps {
   title: string;
@@ -25,11 +25,11 @@ function SimpleCallout({title, children, className}: SimpleCalloutProps) {
         'p-6 xl:p-8 pb-4 xl:pb-6 bg-card dark:bg-card-dark rounded-2xl shadow-inner-border dark:shadow-inner-border-dark text-base text-secondary dark:text-secondary-dark my-8',
         className
       )}>
-      <H3
+      <H2
         className="text-primary dark:text-primary-dark mt-0 mb-3 leading-tight"
         isPageAnchor={false}>
         {title}
-      </H3>
+      </H2>
       {children}
     </div>
   );

src/content/warnings/react-dom-test-utils.md

@@ -44,7 +44,19 @@ import {render} from '@testing-library/react';
 render(<Component />);
 ```
 
-### ReactDOMTestUtils.Simulate {/*reactdomtestutilssimulate*/}
+`render` returns an `unmount` function and the rendered container:
+
+```js
+const {unmount, container} = render(<Component />);
+
+unmount();
+expect(container.innerHTML).toBe('');
+```
+
+React Testing Library automatically cleans up rendered trees after each test when your test framework provides an `afterEach` hook. You can call `unmount` yourself when you need to verify cleanup during a test. Unmounting a tree also removes content rendered into a portal by that tree. If your test creates a separate React root, unmount that root separately.
+
+```
+ ### ReactDOMTestUtils.Simulate {/*reactdomtestutilssimulate*/}
 
 `Simulate` can be replaced with `fireEvent` from `@testing-library/react`.