Add tests to confirm behaviour.

I wasn't able to figure out a test that triggers the original behaviour from this bug but these tests will definitely fail if `key={}` is not there, which is good.

code/jest.config.js

@@ -40,6 +40,7 @@ module.exports = {
   ],
   roots: [
     '<rootDir>/addons',
+    '<rootDir>/renderers',
     '<rootDir>/frameworks',
     '<rootDir>/lib',
     '<rootDir>/examples/official-storybook',

code/renderers/react/src/render.test.tsx

@@ -0,0 +1,58 @@
+import React, { useEffect } from 'react';
+import { jest, describe, it, expect } from '@jest/globals';
+
+import { renderToDOM } from './render';
+
+jest.setTimeout(500);
+
+describe('react renderer', () => {
+  it('waits until the component has rendered', async () => {
+    const domElement = document.createElement('div');
+    const unboundStoryFn = jest.fn(() => 'Story');
+    const showMain = jest.fn();
+
+    await renderToDOM({ unboundStoryFn, showMain } as any, domElement);
+    expect(unboundStoryFn).toHaveBeenCalledTimes(1);
+    expect(domElement.innerHTML).toBe('Story');
+  });
+
+  it('re-renders the story when called again', async () => {
+    const domElement = document.createElement('div');
+    const unboundStoryFn = jest.fn(() => 'Story');
+    const showMain = jest.fn();
+
+    await renderToDOM({ unboundStoryFn, showMain } as any, domElement);
+    await renderToDOM({ unboundStoryFn, showMain } as any, domElement);
+    expect(unboundStoryFn).toHaveBeenCalledTimes(2);
+  });
+
+  it('does not remount the component when called a second time', async () => {
+    const domElement = document.createElement('div');
+    const effect = jest.fn();
+    const Component = () => {
+      useEffect(effect as any, []);
+      return <div>Component</div>;
+    };
+    const unboundStoryFn = jest.fn(() => <Component />);
+    const showMain = jest.fn();
+
+    await renderToDOM({ unboundStoryFn, showMain } as any, domElement);
+    await renderToDOM({ unboundStoryFn, showMain } as any, domElement);
+    expect(effect).toHaveBeenCalledTimes(1);
+  });
+
+  it('does remount the component when called with forceRemount', async () => {
+    const domElement = document.createElement('div');
+    const effect = jest.fn();
+    const Component = () => {
+      useEffect(effect as any, []);
+      return <div>Component</div>;
+    };
+    const unboundStoryFn = jest.fn(() => <Component />);
+    const showMain = jest.fn();
+
+    await renderToDOM({ unboundStoryFn, showMain } as any, domElement);
+    await renderToDOM({ unboundStoryFn, showMain, forceRemount: true } as any, domElement);
+    expect(effect).toHaveBeenCalledTimes(2);
+  });
+});