It's not the tests per se, but it's what is put on the line. Raises, funding, evaluations, keeping your job - these are all disincentives to well-rounded education. Please don't make me quote the plethora of studies that show how important arts, literature, and the sciences are to primary education. Completely stopping studying these things for half the school year is bad.
So it doesn't matter if the tests are filled with good-to-know knowledge - they're positioned to dis-incentivize and devalue anything that isn't math, language arts, and a narrow reading of how to structure an essay.
[0] http://www.usnews.com/opinion/articles/2013/04/11/why-excess...
You raise an objection to raises and funding being tied to test outcomes. Why would this be bad? Sure, if the tests are testing the wrong things, then we should fix the tests. But, it's not impossible to measure educational outcomes. Why should teachers continued employment, and pay, not reflect how well they are measured to be doing, at the thing they are paid to do?
- As I said above, you would need to cite which test question are game-able, and which encourage this narrow teaching, which critics never do.
- If the problem is that teachers try to satisfy this goal by trying to game the tests, then the problem is with this way of teaching, not the tests per se.