to remember that teachers are not in charge of education; we are the scapegoats, and a convenient tool for reformers.
I don't know any teachers who want to give more tests.
I do know that the testing reform culture has been in place long enough at this point to present another danger:
As those of us who can remember teaching without the tests grow older and retire, the up and coming generation of newer teachers will never have experienced broad curriculum not tied to high stakes tests and other mandates. They will think it is "normal" and be less resistant to more and more and more destruction.
This kind of test? Opt out. I'm ambivalent about opting out of the test that is used to punish schools and teachers, because...it punishes schools and teachers who don't have any choice in the matter.
This kind of standardized "formative assessment," or "diagnostic test," though, should not, at this point, have any high-stakes attached. Although, if voters don't stop voting in politicians who support the privatization of public education, I'm sure that's coming soon, too.
Opt out. In writing.
Adding another thought:
Some districts and schools give blanket tests to a grade to find gifted students who would have slid beneath the radar otherwise. Maybe that's what this was, as your description doesn't seem to serve the same purpose as the mandatory formative assessments at my school and district. You can still opt out. If you think your child ought to be identified for services under a gifted ed program, there are other ways to identify.