For the past few years I've taught only two courses--pre-calculus (incl. trig) and statistics. As I'm our school's only stats teacher, I make all the decisions myself. It might be nice to have someone to bounce ideas off of, but I end up doing ok. I share pre-calculus with another teacher, though, and since the latest push is "equal educational experience", or something like that, we try to make our classes as much alike as possible. So far that means collaborating on quizzes and tests, as well as giving them on the same day as each other. It will mean more as time goes on.
The other teacher has a different philosophy of testing than I do. He's more flexible than I am on the topic, though, so thankfully he compromises more than I do! He used to give 2-day tests, now we give 1-day tests, for example. And in many cases I come up with the problems, he types up the test or quiz, and then I format how I like (I like a definite place in which to put the answer, for example). Then we give the assessment.
Recently we've been covering trigonometric sum and difference identities, double-angle and half-angle identities, and the like. He's always been one to require students to memorize the formulas, whereas I'm not one much for memorizing things that students will use only once. I can tell he didn't like compromising on that point, so I threw him a bone: what if, instead of a bonus question on the test, we give bonus points if students opt to take the test without using the list of identities? He liked it, we agreed on his determination of how many "bonus" points to grant for doing so, and that was that.