Add basic e2e test for the most `ContrastChecker` simple cases

[afercia]

Description

After #68799 it would be nice to add at least one e2e test to make sure the ContrastChecker detects and checks colors reliably for the most simple case:

• Add a paragraph with some content.
• Set both background and text colors to black.
• Test that the ContrastChecker notice appears in the block settings panel immediately as soon as the low-contrast color pair is applied.

For the future, it would be nice to expand the ContrastChecker tests when other pending issues will ne solved, they are tracked at #60824

Step-by-step reproduction instructions

N/A

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure

[himanshupathak95]

Hey @afercia, I agree with this proposal and would love to write an e2e test for the ContrastChecker component since I have already written a storybook for the same.

[afercia]

Sure @himanshupathak95 do feel free to go ahead!

[juanfra]

This is great! The code currently detects the background color from parent nodes, so it might be a good idea to test that as well. Specifically, we could check if selecting a text color triggers a warning when it doesn’t meet contrast requirements against the site’s background color.