Add warning page for ReactDOMTestUtils deprecation (#6716)

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

@@ -0,0 +1,87 @@
+---
+title: react-dom/test-utils Deprecation Warnings
+---
+
+## ReactDOMTestUtils.act() warning {/*reactdomtestutilsact-warning*/}
+
+`act` from `react-dom/test-utils` has been deprecated in favor of `act` from `react`.
+
+Before:
+
+```js
+import {act} from 'react-dom/test-utils';
+```
+
+After:
+
+```js
+import {act} from 'react';
+```
+
+## Rest of ReactDOMTestUtils APIS {/*rest-of-reactdomtestutils-apis*/}
+
+All APIs except `act` have been removed.
+
+The React Team recommends migrating your tests to [@testing-library/react](https://testing-library.com/docs/react-testing-library/intro/) for a modern and well supported testing experience.
+
+### ReactDOMTestUtils.renderIntoDocument {/*reactdomtestutilsrenderintodocument*/}
+
+`renderIntoDocument` can be replaced with `render` from `@testing-library/react`.
+
+Before:
+
+```js
+import {renderIntoDocument} from 'react-dom/test-utils';
+
+renderIntoDocument(<Component />);
+```
+
+After:
+
+```js
+import {render} from '@testing-library/react';
+
+render(<Component />);
+```
+
+### ReactDOMTestUtils.Simulate {/*reactdomtestutilssimulate*/}
+
+`Simulate` can be replaced with `fireEvent` from `@testing-library/react`.
+
+Before:
+
+```js
+import {Simulate} from 'react-dom/test-utils';
+
+const element = document.querySelector('button');
+Simulate.click(element);
+```
+
+After:
+
+```js
+import {fireEvent} from '@testing-library/react';
+
+const element = document.querySelector('button');
+fireEvent.click(element);
+```
+
+Be aware that `fireEvent` dispatches an actual event on the element and doesn't just synthetically call the event handler.
+
+### List of all removed APIs {/*list-of-all-removed-apis-list-of-all-removed-apis*/}
+
+- `mockComponent()`
+- `isElement()`
+- `isElementOfType()`
+- `isDOMComponent()`
+- `isCompositeComponent()`
+- `isCompositeComponentWithType()`
+- `findAllInRenderedTree()`
+- `scryRenderedDOMComponentsWithClass()`
+- `findRenderedDOMComponentWithClass()`
+- `scryRenderedDOMComponentsWithTag()`
+- `findRenderedDOMComponentWithTag()`
+- `scryRenderedComponentsWithType()`
+- `findRenderedComponentWithType()`
+- `renderIntoDocument`
+- `Simulate`