I think this is a good test, but the test it replaces was also a good test. In particular, if the referrer policy passed to fetch() is the empty string (the default value), the fetching algorithm will pull the value from the request's client, which is the iframe's global object/document which does have a referrer policy, right? So as far as I can tell both should work.

For the test I replaces, both browsers do not work as you said, which is noted in fetch 4.1.2.5
However, it distracts the spec we want to modify here. We might need another issue for Referrer-Policy to address this.

How about we leave the test in and file bugs against browsers? It does seem like something that ought to be fixed.

I leave both tests in this version. Two observations:
(a) We load too many iframes in one test, which could cause TIME-OUT
(b) In current Firefox, |submit.click();| doesn't work sometimes for the form POST test.

For a) should we split the test somehow then? I could merge this first and then we can do that separately though. Not sure what the problem could be with b).

Let's merge. Thanks!