diff --git a/packages/react-dom/src/__tests__/ReactDOMComponentTree-test.js b/packages/react-dom/src/__tests__/ReactDOMComponentTree-test.js
index f1873882f5c7d..93c081d8d48c6 100644
--- a/packages/react-dom/src/__tests__/ReactDOMComponentTree-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMComponentTree-test.js
@@ -10,114 +10,217 @@
 'use strict';
 
 describe('ReactDOMComponentTree', () => {
-  var React;
-  var ReactDOM;
-  var ReactDOMComponentTree;
-  var ReactDOMServer;
-
-  function renderMarkupIntoDocument(elt) {
-    var container = document.createElement('div');
-    // Force server-rendering path:
-    container.innerHTML = ReactDOMServer.renderToString(elt);
-    return ReactDOM.hydrate(elt, container);
-  }
-
-  function getTypeOf(instance) {
-    return instance.type;
-  }
-
-  function getTextOf(instance) {
-    return instance.memoizedProps;
-  }
+  let React;
+  let ReactDOM;
+  let container;
 
   beforeEach(() => {
     React = require('react');
     ReactDOM = require('react-dom');
-    // TODO: can we express this test with only public API?
-    ReactDOMComponentTree = require('../client/ReactDOMComponentTree');
-    ReactDOMServer = require('react-dom/server');
+    container = document.createElement('div');
+    document.body.appendChild(container);
   });
 
-  it('finds nodes for instances', () => {
-    // This is a little hard to test directly. But refs rely on it -- so we
-    // check that we can find a ref at arbitrary points in the tree, even if
-    // other nodes don't have a ref.
+  afterEach(() => {
+    document.body.removeChild(container);
+    container = null;
+  });
+
+  it('finds nodes for instances on events', () => {
+    const mouseOverID = 'mouseOverID';
+    const clickID = 'clickID';
+    let currentTargetID = null;
+    // the current target of an event is set to result of getNodeFromInstance
+    // when an event is dispatched so we can test behavior by invoking
+    // events on elements in the tree and confirming the expected node is
+    // set as the current target
     class Component extends React.Component {
+      handler = e => {
+        currentTargetID = e.currentTarget.id;
+      };
       render() {
-        var toRef = this.props.toRef;
         return (
-          <div ref={toRef === 'div' ? 'target' : null}>
-            <h1 ref={toRef === 'h1' ? 'target' : null}>hello</h1>
-            <p ref={toRef === 'p' ? 'target' : null}>
-              <input ref={toRef === 'input' ? 'target' : null} />
-            </p>
-            goodbye.
+          <div id={mouseOverID} onMouseOver={this.handler}>
+            <div id={clickID} onClick={this.handler} />
           </div>
         );
       }
     }
 
-    function renderAndGetRef(toRef) {
-      var inst = renderMarkupIntoDocument(<Component toRef={toRef} />);
-      return inst.refs.target.nodeName;
+    function simulateMouseEvent(elem, type) {
+      const event = new MouseEvent(type, {
+        bubbles: true,
+      });
+      elem.dispatchEvent(event);
     }
 
-    expect(renderAndGetRef('div')).toBe('DIV');
-    expect(renderAndGetRef('h1')).toBe('H1');
-    expect(renderAndGetRef('p')).toBe('P');
-    expect(renderAndGetRef('input')).toBe('INPUT');
+    const component = <Component />;
+    ReactDOM.render(component, container);
+    expect(currentTargetID).toBe(null);
+    simulateMouseEvent(document.getElementById(mouseOverID), 'mouseover');
+    expect(currentTargetID).toBe(mouseOverID);
+    simulateMouseEvent(document.getElementById(clickID), 'click');
+    expect(currentTargetID).toBe(clickID);
   });
 
-  it('finds instances for nodes', () => {
-    class Component extends React.Component {
+  it('finds closest instance for node when an event happens', () => {
+    const nonReactElemID = 'aID';
+    const innerHTML = {__html: `<div id="${nonReactElemID}"></div>`};
+    const closestInstanceID = 'closestInstance';
+    let currentTargetID = null;
+
+    class ClosestInstance extends React.Component {
+      _onClick = e => {
+        currentTargetID = e.currentTarget.id;
+      };
       render() {
         return (
-          <div>
-            <h1>hello</h1>
-            <p>
-              <input />
-            </p>
-            goodbye.
-            <main dangerouslySetInnerHTML={{__html: '<b><img></b>'}} />
-          </div>
+          <div
+            id={closestInstanceID}
+            onClick={this._onClick}
+            dangerouslySetInnerHTML={innerHTML}
+          />
         );
       }
     }
 
-    function renderAndQuery(sel) {
-      var root = renderMarkupIntoDocument(
-        <section>
-          <Component />
-        </section>,
-      );
-      return sel ? root.querySelector(sel) : root;
+    function simulateClick(elem) {
+      const event = new MouseEvent('click', {
+        bubbles: true,
+      });
+      elem.dispatchEvent(event);
+    }
+
+    const component = <ClosestInstance />;
+    ReactDOM.render(<section>{component}</section>, container);
+    expect(currentTargetID).toBe(null);
+    simulateClick(document.getElementById(nonReactElemID));
+    expect(currentTargetID).toBe(closestInstanceID);
+  });
+
+  it('updates event handlers from fiber props', () => {
+    let action = '';
+    let instance;
+    const handlerA = () => (action = 'A');
+    const handlerB = () => (action = 'B');
+
+    function simulateMouseOver(target) {
+      const event = new MouseEvent('mouseover', {
+        bubbles: true,
+      });
+      target.dispatchEvent(event);
+    }
+
+    class HandlerFlipper extends React.Component {
+      state = {flip: false};
+      flip() {
+        this.setState({flip: true});
+      }
+      render() {
+        return (
+          <div
+            id="update"
+            onMouseOver={this.state.flip ? handlerB : handlerA}
+          />
+        );
+      }
     }
 
-    function renderAndGetInstance(sel) {
-      return ReactDOMComponentTree.getInstanceFromNode(renderAndQuery(sel));
+    ReactDOM.render(
+      <HandlerFlipper key="1" ref={n => (instance = n)} />,
+      container,
+    );
+    const node = container.firstChild;
+    simulateMouseOver(node);
+    expect(action).toEqual('A');
+    action = '';
+    // Render with the other event handler.
+    instance.flip();
+    simulateMouseOver(node);
+    expect(action).toEqual('B');
+  });
+
+  it('finds a controlled instance from node and gets its current fiber props', () => {
+    const inputID = 'inputID';
+    const startValue = undefined;
+    const finishValue = 'finish';
+
+    class Controlled extends React.Component {
+      state = {value: startValue};
+      a = null;
+      _onChange = e => this.setState({value: e.currentTarget.value});
+      render() {
+        return (
+          <input
+            id={inputID}
+            type="text"
+            ref={n => (this.a = n)}
+            value={this.state.value}
+            onChange={this._onChange}
+          />
+        );
+      }
     }
 
-    function renderAndGetClosest(sel) {
-      return ReactDOMComponentTree.getClosestInstanceFromNode(
-        renderAndQuery(sel),
-      );
+    const setUntrackedInputValue = Object.getOwnPropertyDescriptor(
+      HTMLInputElement.prototype,
+      'value',
+    ).set;
+
+    function simulateInput(elem, value) {
+      const inputEvent = new Event('input', {
+        bubbles: true,
+      });
+      setUntrackedInputValue.call(elem, value);
+      elem.dispatchEvent(inputEvent);
     }
 
-    expect(getTypeOf(renderAndGetInstance(null))).toBe('section');
-    expect(getTypeOf(renderAndGetInstance('div'))).toBe('div');
-    expect(getTypeOf(renderAndGetInstance('h1'))).toBe('h1');
-    expect(getTypeOf(renderAndGetInstance('p'))).toBe('p');
-    expect(getTypeOf(renderAndGetInstance('input'))).toBe('input');
-    expect(getTypeOf(renderAndGetInstance('main'))).toBe('main');
-
-    // This one's a text component!
-    var root = renderAndQuery(null);
-    var inst = ReactDOMComponentTree.getInstanceFromNode(
-      root.children[0].childNodes[2],
+    const component = <Controlled />;
+    const instance = ReactDOM.render(component, container);
+    spyOn(console, 'error');
+    expectDev(console.error.calls.count()).toBe(0);
+    simulateInput(instance.a, finishValue);
+    expectDev(console.error.calls.count()).toBe(1);
+    expectDev(console.error.calls.argsFor(0)[0]).toContain(
+      'Warning: A component is changing an uncontrolled input of ' +
+        'type text to be controlled. Input elements should not ' +
+        'switch from uncontrolled to controlled (or vice versa). ' +
+        'Decide between using a controlled or uncontrolled input ' +
+        'element for the lifetime of the component. More info: ' +
+        'https://fb.me/react-controlled-components',
     );
-    expect(getTextOf(inst)).toBe('goodbye.');
+  });
 
-    expect(getTypeOf(renderAndGetClosest('b'))).toBe('main');
-    expect(getTypeOf(renderAndGetClosest('img'))).toBe('main');
+  it('finds instance of node that is attempted to be unmounted', () => {
+    spyOn(console, 'error');
+    const component = <div />;
+    const node = ReactDOM.render(<div>{component}</div>, container);
+    ReactDOM.unmountComponentAtNode(node);
+    expectDev(console.error.calls.count()).toBe(1);
+    expectDev(console.error.calls.argsFor(0)[0]).toContain(
+      "unmountComponentAtNode(): The node you're attempting to unmount " +
+        'was rendered by React and is not a top-level container. You may ' +
+        'have accidentally passed in a React root node instead of its ' +
+        'container.',
+    );
+  });
+
+  it('finds instance from node to stop rendering over other react rendered components', () => {
+    spyOn(console, 'error');
+    const component = (
+      <div>
+        <span>Hello</span>
+      </div>
+    );
+    const anotherComponent = <div />;
+    const instance = ReactDOM.render(component, container);
+    ReactDOM.render(anotherComponent, instance);
+    expectDev(console.error.calls.count()).toBe(1);
+    expectDev(console.error.calls.argsFor(0)[0]).toContain(
+      'render(...): Replacing React-rendered children with a new root ' +
+        'component. If you intended to update the children of this node, ' +
+        'you should instead have the existing children update their state ' +
+        'and render the new components instead of calling ReactDOM.render.',
+    );
   });
 });