frontend/tests: enzyme dead → react-testing-library

[haraldschilly]

I wanted to add tests for some frontend code, and well, I think there are no working tests right now. I'll tweak this a bit in my i18n branch, but after all, we should clarify their status and update them. There is no "enzyme" package for react 18 any more. Instead, I think the way forward is react-testing-library.

These are the files I'm referring to:

...src/packages/frontend$ git ls-files '**/*.test.tsx'

components/A.test.tsx
jupyter/output-messages/__test__/ansi.test.tsx
jupyter/output-messages/__test__/javascript.test.tsx
jupyter/output-messages/__test__/more-output.test.tsx
jupyter/output-messages/__test__/stderr.test.tsx
jupyter/output-messages/__test__/stdout.test.tsx
jupyter/output-messages/__test__/text-plain.test.tsx
jupyter/output-messages/__test__/untrustred-javascript.test.tsx
misc/__test__/local-storage.test.tsx