**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.
var stack = '';
  if (currentlyValidatingElement) {
    var name = getDisplayName(currentlyValidatingElement);
    var owner = currentlyValidatingElement._owner;
    stack += describeComponentFrame(
      name,
      currentlyValidatingElement._source,
      owner && getComponentName(owner),
    );
  }
  return stack;
}
function getName(type, instance) {
  var constructor = instance && instance.constructor;
  return (
    type.displayName ||
    (constructor && constructor.displayName) ||
    type.name ||
    (constructor && constructor.name) ||
    null
  );
}
function shouldConstruct(Component) {
  return !!(Component.prototype && Component.prototype.isReactComponent);
}
export default ReactShallowRenderer;