Epic: Refactor Test Suite

[drewbo]

As part of a broader React and related dependency upgrade, we likely need to significantly change our current test suite:

• the primary test renderer enzyme does not have a supported adapter for React 18
• the current React recommendation for test frameworks is to use jest and react-testing-library; these seemingly have better integration with newer React features than enzyme or mocha

Notes

• React Testing Overview
• React Testing Environments
• Jest
• React Testing Library
• RTL: migrate from enzyme

### Tasks
- [ ] Create a partial RTL-based testing suite to be run in conjunction with existing test suite
- [ ] Decide on a test coverage threshold or other metric for deciding when to switch over
- [ ] Add code coverage reporting and delta on PR

[drewbo]

Started initial work on this in https://github.com/cloud-gov/pages-core/tree/refactor-test-suite and updated the acceptance criteria

[drewbo]

Update: I rebased the aforementioned branch and made a few updates to get linting + coverage working with latest main. The coverage stats show that this covers roughly 6% of the components and 4% of the whole frontend folder. An assortment of thoughts with no particular end goal:

• Switching from enzyme to RTL (without making changes to the underlying test intent) is a bit of a chore but also maybe could be partially automated with some regex?
• The non-component tests only need to be switched from chai to jest, which is mostly a matter of different assertion names. This is also a bit of a chore and maybe could be partially automated.
• The test logic itself probably needs a once over. That seems like a big undertaking to do all at once, maybe it could happen in conjunction with component updates on some sort of ongoing basis