why does the testname format does not support icons?

I am reading the codebase after few attempts at finding the incantation to make this work, and took a hint on the fact that in the tests the icons are only tested against the `pkgname` format.

Is there a reason why this doesn't work? Or better, did I miss something in the docs?

Start by reading the tests that cover icons for the `pkgname` format and the documentation describing `testname` formats. Determine whether icon support is intentionally limited or missing, then update the relevant behavior or docs so the supported formats and expected output are clear.

Written by the indexing model from the issue text.