**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.
state = {clicked: false};
      onClick = () => {
        this.setState({clicked: true});
      };
      render() {
        const className = this.state.clicked ? 'was-clicked' : '';
        if (this.props.aNew === 'prop') {
          return (
            <a href="#" onClick={this.onClick} className={className}>
              Test link
            </a>
          );
        } else {
          return (
            <div>
              <span className="child1" />
              <span className="child2" />
            </div>
          );
        }
      }
    }