We purge it [here](https://github.com/facebook/react/blob/b11540ccb2321aeb7259fcf0b3a38aeeea35231d/src/isomorphic/ReactDebugTool.js#L88-L89) but this code doesn’t run because of the [early exit](https://github.com/facebook/react/blob/b11540ccb2321aeb7259fcf0b3a38aeeea35231d/src/isomorphic/ReactDebugTool.js#L53-L57).

Need to fix this and add a test case to make sure we don’t regress on it.

expect(getActualTree()).toBe(undefined);
    expect(getRootDisplayNames()).toEqual([]);
    expect(getRegisteredDisplayNames()).toEqual([]);
    
    
    pairs.forEach(([element, expectedTree]) => {
      currentElement = element;
      ReactDOMServer.renderToString(<Wrapper />);
      expect(getActualTree()).toEqual(expectedTree);
      ReactComponentTreeDevtool.purgeUnmountedComponents();
      expect(getActualTree()).toBe(undefined);
      expect(getRootDisplayNames()).toEqual([]);
      expect(getRegisteredDisplayNames()).toEqual([]);
    });
  }
  describe('mount', () => {
    it('uses displayName or Unknown for classic components', () => {
      var Foo = React.createClass({
        render() {
          return null;
        },
      });
      Foo.displayName = 'Bar';
      var Baz = React.createClass({
        render() {
          return null;
        },
      });
      var Qux = React.createClass({
        render() {