A couple of thoughts

`Range: bytes=0-` can be interpreted by servers as "the whole thing", so it's not surprising that they might think they can send back a 200. A more interesting test would be something like `Range: bytes=20-200` (depending on the size of the response body).

Also, I very much wonder if anything would change if you send `If-Range`...

Reproduce the request with `Range: bytes=20-200` and compare the server response with the existing `bytes=0-` case. Then investigate whether adding `If-Range` changes the result. Done means the relevant range and conditional-range behavior is covered by the test setup.

Written by the indexing model from the issue text.