Add continuout native event test

packages/react-dom/src/__tests__/ReactDOMNativeEventHeuristic-test.js

@@ -284,6 +284,46 @@ describe('ReactDOMNativeEventHeuristic-test', () => {
     expect(container.textContent).toEqual('hovered');
   });
 
+  // @gate experimental
+  it('continuous native events flush as expected', async () => {
+    const root = ReactDOM.unstable_createRoot(container);
+
+    const target = React.createRef(null);
+    function Foo({hovered}) {
+      const hoverString = hovered ? 'hovered' : 'not hovered';
+      Scheduler.unstable_yieldValue(hoverString);
+      return <div ref={target}>{hoverString}</div>;
+    }
+
+    await act(async () => {
+      root.render(<Foo hovered={false} />);
+    });
+    expect(container.textContent).toEqual('not hovered');
+
+    await act(async () => {
+      // Note: React does not use native mouseenter/mouseleave events
+      // but we should still correctly determine their priority.
+      const mouseEnterEvent = document.createEvent('MouseEvents');
+      mouseEnterEvent.initEvent('mouseover', true, true);
+      target.current.addEventListener('mouseover', () => {
+        root.render(<Foo hovered={true} />);
+      });
+      dispatchAndSetCurrentEvent(target.current, mouseEnterEvent);
+
+      // Since mouse end is not discrete, should not have updated yet
+      expect(Scheduler).toHaveYielded(['not hovered']);
+      expect(container.textContent).toEqual('not hovered');
+
+      expect(Scheduler).toFlushAndYieldThrough(['hovered']);
+      if (gate(flags => flags.enableSyncDefaultUpdates)) {
+        expect(container.textContent).toEqual('hovered');
+      } else {
+        expect(container.textContent).toEqual('not hovered');
+      }
+    });
+    expect(container.textContent).toEqual('hovered');
+  });
+
   // @gate experimental
   it('should batch inside native events', async () => {
     const root = ReactDOM.unstable_createRoot(container);