Update Jest to 26.x for better API support

[bryceosterhaus]

Issue type (mark with x)

• 🎁 Feature request

Description

With our new support matrix for browsers, I think it would be helpful to update Jest to 26.x so that we can get better js-dom support.

I was adding document.createRange and createContextualFragment and I realized that our current version of Jest does not support those APIs. I saw on this issue that 26.x should now support those.

[wincent]

I think this is duplicate of #46 — note that we have been holding off on the update due to still-existing performance regressions introduced in Jest v25. We actually did do an update at one point, although I don't have the link at hand, that was so bad that we had to roll it back (because the perf was so bad it made the tests time out).

[bryceosterhaus]

@wincent yep you're right, didn't see that one. Thanks!

[jbalsas]

One option would be to simply mock createContextualFragment with exactly what metal-dom does in buildFragment.

That way we can start using it and jest will know how to handle until we update it.

[wincent]

One option would be to simply mock createContextualFragment with exactly what metal-dom does in buildFragment.

@bryceosterhaus did this in #234

I made a note in #46 reminding us to remove the mock once it's no longer needed.