The obvious starting points would be Jest for unit tests and either Cypress or Playwright for e2e. A year ago I would have recommended Playwright pretty unequivocally and I still would if you want to test multiple languages with the same syntax/framework. Otherwise, Cypress now has component testing that obviates React Testing Library. That is a pretty nice thing to have together in the same framework and Cypress has made their UX really nice in the last few releases.
From https://github.com/gadomski/heystac/pull/8#issuecomment-2443952675: