Tests

Does anyone have experience in writing tests with hooks? There should be no need to test the part that Final Form does (e.g. does a field become dirty when the value changes), but we need _something_ in place to evaluate new features as they get added, and to ensure that a PR doesn't break the whole library.

Maybe something [along these lines](https://github.com/donavon/use-dark-mode/blob/develop/__tests__/index.test.js)?

If anyone would like to give this a shot, it would be greatly appreciated! 🙏

Start by reviewing the linked use-dark-mode __tests__/index.test.js example and the repository's current test setup. Define coverage for evaluating new hook features and catching regressions without duplicating Final Form's behavior; done means a maintainable test suite is in place and runs successfully.

Written by the indexing model from the issue text.