Yes, we took the 2nd grade CAT test (actually the CAT 5 Survey, a shorter test but just as acceptable here) because in WA, 8yo is the age we need to start. We found the second grade level for that test to be laughably easy.
Ways I made it easier for dd, because she wasn't familiar with the format was to atlk to her about what was wanted. That was easy, because there is a script the parent (or test administrator) is supposed to follow. I had no ethical qualms with helping her understand what the test needed from her. (I also absolutely do not care that this might bump up her scores because a lot of school kids got an answer wrong not because they didn't know the material but because they misunderstood what was being asked.)
I also had no qualms about letting her pick up and put down the test as necessary, within the time limits we had to return the test and the materials (2 weeks). Some days we zoomed through 2 sections, she was having so much fun (yes, it was enormously fun for her). A couple of sections we moved through slowly.
Once again, I didn't lead her to answers, but I made sure she went carefully through the questions and all the answers, then let her make mistakes as necessary. I tried keeping my nose in the administrator's script to avoid putting undue pressure on her, but I don't think she was feeling it. (As much as I love unschooling, I still have a lot of deschooling to do!) I let her know quite clearly that we were just learning how to take a test, and that was exactly how I approached it. She did marvelously and had a lot of fun. Her spelling scores were dismal, but then we never focused on spelling much.
It helped for me that in our state the test results are for the parent alone. But now that I've been through that test, I would have no troubles facing it down again. I don't think this particular CAT test is very indicative of what kindergarten is doing today. Maybe other versions of the CAT that might be required elsewhere would be different. Anyway, that was our experience. I admit, a lot of stress over nothing, it turned out.
ETA: I also stressed about evaluation vs. test, and decided that the test would be less intrusive, and I wouldn't accidentally bring more academic pressure into my home by selecting the "wrong" evaluator. Testing was simple, private, and in the end much easier and less intrusive than I ever imagined.