feat: Simulators for async testing

[zetlen]

Based on my comment here and @jimbo feeling positive about the idea, I've written a couple of helper components. They address a need we already have, and they help us round out Peregrine's starter collections.

From README:

• <DelayedValue initial={empty}, delay={2000}, updated={full}> – Passes updated props to its children on a timer. Test progressive load states!
• <MultipleTimedRenders schedule> – Configurable with a schedule array to update child props multiple times on successive timers. For more complex scenarios than DelayedProps.

[DrewML]

Missing an export in src/index.js - we don't want consumers to have to reach into @magento/peregrine/dist/*

[zetlen]

@jimbo @jcalcaben @DrewML Checking in: have my updates fixed the issues you found?

[DrewML]

In the future, would super appreciate if we could split something like this into separate PRs we iterate on. One of these components builds on the other, so it seems like a fairly natural progression.

Would make landing this much easier.

[PWAStudioBot]

All tests passed! View Coverage Report

A Storybook for this PR has been deployed!. It will be accessible as soon as the current build completes.

Generated by :no_entry_sign: dangerJS

[zetlen]

Any advice on how to generate a Storybook for this? Or, if that's not gating merge...we good?

[DrewML]

Any advice on how to generate a Storybook for this

Any nested dir with the name __stories__ in src will get picked up by storybook. You can look at the other story in the repo and examples in Storybook's docs.

if that's not gating merge

I wouldn't say it's gating merge since this PR was opened prior to the introduction of Storybook. Having said that, this is something that would actually be beneficial to have in Storybook, and I don't know how many people are going to use it without. Use your best judgement whether it should be in this PR or a follow-up.

[zetlen]

Thanks. I think we ought to have it in a followup, since the PR is already big enough. I can backlog that--I'm sure we'll have lots of PRs in the future that do nothing but improve testing and coverage.

[DrewML]