I had a question about halal/breathable nail polish. There are brands that say water can go through nail polish therefore we can do wudhu whilst wearing the nail polish. Is this allowed? And how would we test it to be sure the water goes through?

Yes I’m aware of these brands. After some research, eg Inglot, it’s hard to be sure. Some say it’s breathable and other tests say no. Some ladies have told me it depends how many coats of it you apply. The final decision is up to you. If you’re satisfied through research that it is you can use it and do wudhu. Precaution is best way however

I had a question about halal/breathable nail polish. There are brands that say water can go through nail polish therefore we can do wudhu whilst wearing the nail polish. Is this allowed? And how would we test it to be sure the water goes through? Would we need to test it for ourselves or just give if benefit of the doubt?

If the claim is positive and genuine, then yes, but I have no idea how you can prove it. It is better to avoid such things, if you are in doubt.
However, females can test it during their period time.