**Do you want to request a *feature* or report a *bug*?**
report a bug

**What is the current behavior?**
When I call setState with a callback in a test using react shallow renderer (via enzyme), the callback gets called and `this.state` is still the old state.

EDIT: This seems limited to componentWillMount

**If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem via https://jsfiddle.net or similar (template for React 16: https://jsfiddle.net/Luktwrdm/, template for React 15: https://jsfiddle.net/hmbg7e9w/).**

EDIT: Reproduce with this https://github.com/bdwain/setstate-callback-bug

**What is the expected behavior?**
When the setState callback gets called, it should have access to the new state.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
Version 16.
It worked in v15 with enzyme 2.

EDIT: I think this is because in componentWillMount, [this line](https://github.com/facebook/react/blob/master/packages/react-test-renderer/src/ReactShallowRenderer.js#L67) causes the render method in the shallow wrapper to return early, before it updates the state.
});
  it('should react to state changes from callbacks', () => {
    var instance = ReactTestUtils.renderIntoDocument(<MorphingComponent />);
    var el = ReactDOM.findDOMNode(instance);
    expect(el.tagName).toBe('A');
    ReactTestUtils.Simulate.click(el);
    el = ReactDOM.findDOMNode(instance);
    expect(el.tagName).toBe('B');
  });
  it('should rewire refs when rendering to different child types', () => {
    var instance = ReactTestUtils.renderIntoDocument(<MorphingComponent />);
    expect(ReactDOM.findDOMNode(instance.refs.x).tagName).toBe('A');
    instance._toggleActivatedState();
    expect(ReactDOM.findDOMNode(instance.refs.x).tagName).toBe('B');
    instance._toggleActivatedState();
    expect(ReactDOM.findDOMNode(instance.refs.x).tagName).toBe('A');
  });
  it('should not cache old DOM nodes when switching constructors', () => {
    var container = document.createElement('div');
    var instance = ReactDOM.render(
      <ChildUpdates renderAnchor={true} anchorClassOn={false} />,
      container,
    );
    ReactDOM.render(
      
      <ChildUpdates renderAnchor={true} anchorClassOn={true} />,
      container,
    );
    ReactDOM.render(