Add rudimentary test renderer

[sophiebits]

No description provided.

[zpao]

Nothing exposed and we can iterate before we support anything so go go go.

[iamdustan]

extra jsdoc blocks (rootId and containerTag)

[sophiebits]

cc @cpojer

[cpojer]

Awesome. We'll hook this up with snapshot testing over the next two weeks and make a Jest release in about 1.5 weeks from now and also post a nice blog post about snapshot testing. This is gonna be great for react-dom, react-native and any other render target testing.

[cpojer]

Also cc @thejameskyle – @spicyj is adding a field to typecheck whether this is a test render instance, in pretty-format we can then do:

// Jest:
expect(rendered).toMatchSnapshot();

// pretty-format:
if (value.$$typeof == 'react.test-render') {
  formatAsJSXLike(value.toJSON);
}

this is gonna be great.

[sophiebits]

Let's hold off on any public announcement until we solidify the APIs and try it at Facebook some.

[cpojer]

Yep, that is the plan but @gaearon tweeted about it already!

To everyone: please give us two weeks until we can better explain what this is, to show how it works and so we can explain which API guarantees we are providing in React and in Jest.

[bruderstein]

Have I understood correctly that this cannot be used together with the DOM renderer, because of the injection? i.e. once your node process has required this, then using both this and (for instance) TestUtils.renderIntoDocument in the same test file isn't possible, as GenericComponentClass and others have already been injected?

Or am I missing something?

(+1 on having a $$typeof or similar so we can identify the JSON and pretty print in assertion libraries, I tripped over this building support into unexpected-react)