Naomi,
As to anxiousness by the students, remember that a pretest has no standard format. It can designed any way an instructor desires. For instance, it could be an oral test, or a 1-2 question essay, or 5-simple multiple choice questions. One way you could make it interesting is to add a fun, non-serious question here or there to make it more interesting. My pretests are usually about 25 mutiple choice questions that sample portions of my entire course. Also, my pretest is not graded, so I feel students are more willing to put their whole effort into it.
Barry Westling