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

**What is the current behavior?**
This addresses a bug in `enzyme`, https://github.com/airbnb/enzyme/issues/1683.

On [this line](https://github.com/facebook/react/blob/master/packages/react-test-renderer/src/ReactShallowRenderer.js#L110) `element.type()` invokes the SFC with `element` as the `this` value. I believe that this is needed for create-react-class components, but that there needs to be a separate branch for SFCs.

**What is the expected behavior?**
`this` inside a strict-mode SFC will be `undefined`, not the element.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
In all of React 0.13, 0.14, 15, and 16, this bug exists.

While the bug ideally will be fixed, I understand that it's highly unlikely that it would be backported to the 14/15 lines - but I can wrap around it if there's a reliable way, in those versions, to distinguish SFCs from create-react-class components (is there?).
const shallowRenderer = createRenderer();
    shallowRenderer.render(<Component />);
    const mountedInstance = shallowRenderer.getMountedInstance();
    mountedInstance.setState({hasUpdatedState: true}, () => {
      expect(mockFn).toBeCalled();
      expect(mountedInstance.state.hasUpdatedState).toBe(true);
      done();
    });
  });
  it('throws usefully when rendering badly-typed elements', () => {
    const shallowRenderer = createRenderer();
    const renderAndVerifyWarningAndError = (Component, typeString) => {
      expect(() => {
        expect(() => shallowRenderer.render(<Component />)).toWarnDev(
          'React.createElement: type is invalid -- expected a string ' +
            '(for built-in components) or a class/function (for composite components) ' +
            `but got: ${typeString}.`,
        );
      }).toThrowError(
        'ReactShallowRenderer render(): Shallow rendering works only with custom ' +
          `components, but the provided element type was \`${typeString}\`.`,
      );
    };
    renderAndVerifyWarningAndError(undefined, 'undefined');
    renderAndVerifyWarningAndError(null, 'null');
    renderAndVerifyWarningAndError([], 'array');
    renderAndVerifyWarningAndError({}, 'object');
  });
  it('should have initial state of null if not defined', () => {
    class SomeComponent extends React.Component {