How does college board or act "test" their questions?

Just curious if anyone knows how the CB or ACT “test” their questions? Are there “test” or “sample” questions on any of the tests they give that don’t count?

When I took the ACT, we took a section of questions at the end that did not count towards our total score. I believe CB uses the demographic information they collect to find and throw out biased questions, but I’ve never participated in a direct “test” of the questions like I have for the ACT.

@ski_racer thank you! So then you actually took “sample” questions for the ACT. I wonder if the CB does same thing or would they add in or have questions on the PSAT or SAT that maybe are answered during the regular tests, but “not” counted?? Very curious if others know. Thank you again