There is no extra guard or clause in `enqueueForceUpdate` when calling `render` which means the `render` always calls `shouldComponentUpdate` which can block even forced re-render during tests.

This for example [breaks shallow rendering in Enzyme when using MobX and observables](https://github.com/airbnb/enzyme/issues/1267).

Minimal test case:

```javascript
import React from 'react'
import ShallowRenderer from 'react-test-renderer/shallow';
const renderer = new ShallowRenderer();

class TestComponent extends React.Component {
  render() { return <span/> }
}

describe('forceUpdate', () => {
  it('does not call shouldComponentUpdate', () => {
    let called = 0
    TestComponent.prototype.shouldComponentUpdate = () => called += 1
    const component = renderer.render(<TestComponent/>);
    renderer._instance.forceUpdate()
    expect(called).toBe(0) // <- this throws because called === 1
  })
})
```
static contextTypes = {
        name: PropTypes.string,
      };
      render() {
        return <div />;
      }
    }
    const shallowRenderer = createRenderer();
    const result = shallowRenderer.render(<SimpleComponent />);
    expect(result).toEqual(<div />);
  });
  it('passes expected params to component lifecycle methods', () => {
    const componentDidUpdateParams = [];
    const componentWillReceivePropsParams = [];
    const componentWillUpdateParams = [];
    const setStateParams = [];
    const shouldComponentUpdateParams = [];
    const initialProp = {prop: 'init prop'};
    const initialState = {state: 'init state'};
    const initialContext = {context: 'init context'};
    const updatedState = {state: 'updated state'};
    const updatedProp = {prop: 'updated prop'};
    const updatedContext = {context: 'updated context'};
    class SimpleComponent extends React.Component {