I always do every examination paper I ask my students to take and I know many other teachers who routinely do the same.
I like to provide my students with a set of solutions the following day so they can reassure themselves about how they have performed. This process also helps me to make sure I have covered every aspect of the course in my teaching (if not, I make a mental note to do better next year!) and I can speak with authority about how frequently a particular topic is examined.
However, assessing subject knowledge would not tell Ofsted anything much about the effectivess of a particular teacher in a classroom. I have observed many extremely well qualified individuals completely fail to engage at any level with their students.