return the test in storyshots to respect promises.

[travisbloom]

What I did

Jest will wait for promises to resolve before evaluating a test if you return one. This change allows developers to do async work in their test fn

How to test

initStoryshots({
    test: ({ story, context }) => {
        // In the component that is rendered, do some async task that updates the UI after initial render
        const storyElement = story.render(context);
        const tree = renderer.create(storyElement, {});
        return new Promise(resolve => {
            setTimeout(() => {
                const json = tree.toJSON();
                expect(json).toMatchSnapshot();
                resolve();
            }, 0);
        });
    },
});

[codecov]

Codecov Report

Merging #2218 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master    #2218   +/-   ##
=======================================
  Coverage   21.44%   21.44%           
=======================================
  Files         263      263           
  Lines        5801     5801           
  Branches      692      695    +3     
=======================================
  Hits         1244     1244           
+ Misses       4036     4025   -11     
- Partials      521      532   +11

Impacted Files	Coverage Δ
addons/storyshots/src/index.js	0% <0%> (ø)	⬆️
app/react/src/server/config/babel.js	0% <0%> (-100%)	⬇️
app/react/src/server/babel_config.js	0% <0%> (-77.42%)	⬇️
lib/ui/src/modules/ui/containers/down_panel.js	23.52% <0%> (ø)	⬆️
lib/codemod/src/transforms/update-addon-info.js	50% <0%> (ø)	⬆️
...codemod/src/transforms/update-organisation-name.js	40.62% <0%> (ø)	⬆️
...s/left_panel/stories_tree/tree_decorators_utils.js	45.23% <0%> (ø)	⬆️
lib/components/src/navigation/menu_link.js	0% <0%> (ø)	⬆️
addons/knobs/src/components/types/Number.js	8.06% <0%> (ø)	⬆️
addons/knobs/src/components/types/Color.js	8.1% <0%> (ø)	⬆️
... and 20 more

---

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[danielduan]

This looks reasonable to me. I'm not all too familiar with storyshots though.

Anyone with second opinions?

[ndelangen]

That's a great catch @travisbloom !

Fantastic contribution, than you so much 🙇