fix(setData): allow empty objects to be set fix #1704

[Haroenv]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

if someone relied on empty objects not updating, that now no longer makes sense

The PR fulfills these requirements:

• It's submitted to the dev branch.
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue-test-utils/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

This is a tentative fix to show one possible solution, I can clean it up if you think it makes sense

[lmiller1990]

Seems like some tests are failing. LMK if I can help out with anything.

[Haroenv]

I didn't update the tests yet, but I'm more wondering if my approach makes sense, and whether this is a problem that should even be fixed @lmiller1990 :)

[lmiller1990]

I guess so, if Vue supports this (which it does, right, settings something in data to {} will not lose reactivity), it seems like VTU probably should too.

[Haroenv]

Tests are passing now, although I didn't add a new test for this yet :)

[lmiller1990]

Great. Can you add a test for this, too? Then we can merge it.

[Haroenv]

voilà @lmiller1990, new test added :)

[afontcu]

🎉

[Haroenv]

Thanks for your reactivity all 👍