Some very trivial parts of K-12 math can be tested, but they are the least important, imo. The main purpose of high-school math isn't to have students memorize trigonometry formulas: honestly, it doesn't really matter whether high-school students memorize trigonometry formulas or not. The main purpose that might actually have some benefit is to get kids thinking mathematically, and hopefully some proportion of them interested in STEM careers.
Same with high-school CS. You're not really going to learn a lot of specifics in high-school CS, and what specifics you learn are unlikely to be that important. What's important is to learn computational thinking. The tests, however (at least when I took the AP CS test) only tested trivialities, stuff like the syntax of a particular corner of the C++ STL, and the course was therefore set up mainly around that. We literally spent about a month on minutae of iostreams! In an introductory course where most of the students had never programmed before! I could hardly imagine a more stupid way to teach introductory CS, and can't imagine it could've been invented except via ease-of-testing brain damage.
Same with high-school CS. You're not really going to learn a lot of specifics in high-school CS, and what specifics you learn are unlikely to be that important. What's important is to learn computational thinking. The tests, however (at least when I took the AP CS test) only tested trivialities, stuff like the syntax of a particular corner of the C++ STL, and the course was therefore set up mainly around that. We literally spent about a month on minutae of iostreams! In an introductory course where most of the students had never programmed before! I could hardly imagine a more stupid way to teach introductory CS, and can't imagine it could've been invented except via ease-of-testing brain damage.