Could you rebase this branch to get rid of the commits that were already merged to the main branch in older PRs?

@lkleuver I'm trying to build a test similar to the example in the React Testing Library docs and am running into two issues.

1. There's no easy way to add a handler to the mock that overrides the default ones for a specific test.

2. I extended VotersAndVotesForm.test.tsx to click the button and check for the success and/or error element in the page. Even after I make sure startMockAPI() is not called in app/main.tsx, when I run the test, the DOM still contains <p>id="success">Success</p>. So it seems the mock returns a response, even though it's not running?

The only way so far I've found to get the error <p>-element in the DOM is by changing the pollingStationDataEntryHandler to return a 422 if "voters_counts" in json.data.

I think I fixed the current CI error in 7f8658a but that commit got replaced by an older one by accident. Could you rebase and pick 7f8658a instead of cc49795?

The failing Vercel check can be ignored, this is a remnant of me testing Vercel for PR deploys. I'm testing this in a test repository instead :)