Add a regression test for #10906

src/renderers/dom/shared/eventPlugins/__tests__/EnterLeaveEventPlugin-test.js

@@ -13,13 +13,15 @@ var EnterLeaveEventPlugin;
 var React;
 var ReactDOM;
 var ReactDOMComponentTree;
+var ReactTestUtils;
 
 describe('EnterLeaveEventPlugin', () => {
   beforeEach(() => {
     jest.resetModules();
 
     React = require('react');
     ReactDOM = require('react-dom');
+    ReactTestUtils = require('react-dom/test-utils');
     // TODO: can we express this test with only public API?
     ReactDOMComponentTree = require('ReactDOMComponentTree');
     EnterLeaveEventPlugin = require('EnterLeaveEventPlugin');
@@ -58,4 +60,38 @@ describe('EnterLeaveEventPlugin', () => {
     expect(enter.target).toBe(div);
     expect(enter.relatedTarget).toBe(iframe.contentWindow);
   });
+
+  // Regression test for https://github.com/facebook/react/issues/10906.
+  it('should find the common parent after updates', () => {
+    let parentEnterCalls = 0;
+    let childEnterCalls = 0;
+    let parent = null;
+    class Parent extends React.Component {
+      render() {
+        return (
+          <div
+            onMouseEnter={() => parentEnterCalls++}
+            ref={node => (parent = node)}>
+            {this.props.showChild &&
+              <div onMouseEnter={() => childEnterCalls++} />}
+          </div>
+        );
+      }
+    }
+
+    const div = document.createElement('div');
+    ReactDOM.render(<Parent />, div);
+    // The issue only reproduced on insertion during the first update.
+    ReactDOM.render(<Parent showChild={true} />, div);
+
+    // Enter from parent into the child.
+    ReactTestUtils.simulateNativeEventOnNode('topMouseOut', parent, {
+      target: parent,
+      relatedTarget: parent.firstChild,
+    });
+
+    // Entering a child should fire on the child, not on the parent.
+    expect(childEnterCalls).toBe(1);
+    expect(parentEnterCalls).toBe(0);
+  });
 });