Test renderer options

[ndelangen]

This PR replaces: #896

---

Issue:
When running storyshots with a story for a component that uses refs, it will throw a null reference error (see facebook/react#7371)

What I did

This PR adds the ability to pass options to the react-test-renderer create method, for example to allow mocking refs as per https://facebook.github.io/react/blog/2016/11/16/react-v15.4.0.html#mocking-refs-for-snapshot-testing

How to test

Run yarn test - ComponentWithRef.stories.js should use the createNodeMock function defined in storyshots.test.js to mock its ref and not fail with a null reference error. The story for ComponentWithRef attempts to get the scrollWidth of a div when the component mounts.

[ndelangen]

@tmeasday Can you review and test this?

[tmeasday]

Hey @ndelangen

1. I think you missed a key line in rebasing this PR: jrdrg@af02d80#diff-5c231c3fa2827654dca8a602336f00a9 (I'm guessing it got messed up the merge).

2. I suspect the solution of providing a single createNodeMock implementation is probably not going to scale to large projects (each story is probably going to want to provide it's own createNodeMock). So I think @theinterned's idea of story metadata in Allow passing options to storiesOf().add() as hook to customizing story behaviour in plugins #993 is probably the way forward on this.

3. In the meantime, we can use the new test option to achieve the behavior allowed by this PR I think:

import initStoryshots from '@storybooks/addon-storyshots';
import renderer from 'react-test-renderer';

const createNodeMock = () => {
 // ...
]

initStoryShots({
  test({ story, context }) {
    const storyElement = story.render(context, { createNodeMock });
    const tree = renderer.create(storyElement).toJSON();
    expect(tree).toMatchSnapshot();
  }
});

@jrdrg -- I wonder if the above works for you with the latest alpha?

4. I'll work to bring this test case across to test-cra and prove the above works.

[tmeasday]

Perhaps the snapshot test-body should be a higher-order function that takes options as an argument and produces a test-body?

[tmeasday]

I think this can be closed as it's superceded by #1090