You'll notice that the person from Choice states that analysis was complicated and that they may test premium food depending on how the first analysis went.
I don't have permission to link as I am a new member (?) Place this after the url when you get to the site.
about-us/testing-at-choice
It's "what's coming up".
The rest of the information comes from the comments in "Pet food buying guide". If you search for that in their search field you will see two pages of comments. You need to read through the answers.
They also say that the analysis was more complicated than they realised (or words to that effect) and they also said that they may perform an analysis of premium food at a later date, I'm not holding my breath because they seem to have began the supermarket food analysis in early April.
I'm notoriously bad at expressing myself so I appologise if my directions are unclear.