Well, why do you think they are tested? Common Core has defined things students should know. The tests are to gauge whether the students are learning what the Common Core has defined as important. 

Icon, take look at the Springfield School District's curriculum and tell me what year the 8 parts of speech are taught? Tell me what year students are taught that there are 3 branches of government. Do some digging; make some phone calls. See if you can find out when even the most obvious and essential knowledge and skills are taught. Guess what? You won't ever find it. It's simply up to each teacher to decide what he or she wants to teach. I'll bet half the teaching force of Springfield couldn't even name the 3 branches of government or the 8 parts of speech. Common Core and the related testing are trying to change this unfortunate fact!