Additional findDOMNode tests

This is failing in Fiber without the fix. Because we have no deletions to rely
on in this case and the placement effects have already happened.

src/renderers/dom/fiber/__tests__/ReactDOMFiber-test.js

@@ -459,5 +459,29 @@ describe('ReactDOMFiber', () => {
       expect(portalContainer.innerHTML).toBe('<div>changed-changed</div>');
       expect(container.innerHTML).toBe('');
     });
+
+    it('findDOMNode should find dom element after expanding a fragment', () => {
+      class MyNode extends React.Component {
+        render() {
+          return (
+            !this.props.flag ?
+            [<div key="a" />] :
+            [<span key="b" />, <div key="a" />]
+          );
+        }
+      }
+
+      var container = document.createElement('div');
+
+      var myNodeA = ReactDOM.render(<MyNode />, container);
+      var a = ReactDOM.findDOMNode(myNodeA);
+      expect(a.tagName).toBe('DIV');
+
+      var myNodeB = ReactDOM.render(<MyNode flag={true} />, container);
+      expect(myNodeA === myNodeB).toBe(true);
+
+      var b = ReactDOM.findDOMNode(myNodeB);
+      expect(b.tagName).toBe('SPAN');
+    });
   }
 });

src/renderers/dom/shared/__tests__/findDOMNode-test.js

@@ -34,6 +34,32 @@ describe('findDOMNode', () => {
     expect(mySameDiv).toBe(myDiv);
   });
 
+  it('findDOMNode should find dom element after an update from null', () => {
+    function Bar({ flag }) {
+      if (flag) {
+        return <span>A</span>;
+      }
+      return null;
+    }
+    class MyNode extends React.Component {
+      render() {
+        return <Bar flag={this.props.flag} />;
+      }
+    }
+
+    var container = document.createElement('div');
+
+    var myNodeA = ReactDOM.render(<MyNode />, container);
+    var a = ReactDOM.findDOMNode(myNodeA);
+    expect(a).toBe(null);
+
+    var myNodeB = ReactDOM.render(<MyNode flag={true} />, container);
+    expect(myNodeA === myNodeB).toBe(true);
+
+    var b = ReactDOM.findDOMNode(myNodeB);
+    expect(b.tagName).toBe('SPAN');
+  });
+
   it('findDOMNode should reject random objects', () => {
     expect(function() {
       ReactDOM.findDOMNode({foo: 'bar'});