The other day, I talked about the various kinds of speaking tests for English language learners, but I didn't specifically talk about what I did this semester. Here's what happened in my course for first year students in the English major at my uni:
I gave the students 6 possible topics, which were very general in nature and included things like, "Home and Family" or "Health and Exercise" and they were essentially what we had covered in class during the previous weeks.
The students came to my office in groups of 4, and then I randomly assigned them a partner and a topic. The first 2 students had to talk about their first topic for a total of 2-3 minutes, and then the other topic for another 2-3 minutes. Each person in the group had to start off one of the mini-conversations. I only listened and quite rarely had to intervene (only in the case of someone giving 1-2 word answers and not asking any questions in return). Then the next set of partners had their conversation about their 2 topics.
I graded them on a 5 point scale on 3 things:
1. Grammar/Vocab use (only what we had studied in class).
2. Interesting, detailed answers (sentences +an extra detail or two)
3. Appropriate questions/ability to keep the conversation going.
Overall, this round of tests went very well. I was able to evaluate about 25 students in just under 2 hours. I finished not feeling totally exhausted, like I would have if I had had individual conversations will all those students.
I think it was a good balance between random and predictable. It was predictable in that the students had the 6 possible topics before the test, and they knew their 3 potential partners beforehand. But, it was random in that the topics were randomly assigned, as well as the partner, so although students could prepare to some degree, they couldn't just memorize a dialogue.
One thing I didn't like was that the weaker students who gave one or two word answers and didn't ask a lot of questions made the test quite difficult for their partner, although I definitely took this into account during the grading. But, the students are all English majors so there are actually no truly terrible students in the class and most of them have at least a basic proficiency in English, as is not always the case in classes like mandatory Freshman English.