Query and submission guidelines are not meant as a test for authors. But how you follow those guidelines does show us what you will be like to work with as an author.
I ask for specific things when I request material from an author. For fiction, I will always request a synopsis. For nonfiction, I want to see a full proposal. The reasons are because that’s the material I need to be able to make an informed decision about representation. While the material is the first thing I look at, how easy it is to get that material says a lot about an author.
Most of the time authors submit material as requested and I don’t think twice about what the author will be to work with. However, every once in a while I get someone who refuses to write the proposal or submit a synopsis. An author who is unwilling to provide any of those things shows me that going forward there are going to be a lot they might be unwilling to do. Like revisions, or cover copy, or publicity.
So while we would never call the submission process a test, it is a bit like an interview process and how you present yourself as the author gives an indication of what kind of business partner you’ll be.