Hi.
How about a quiz.
It can still be a proper and serious measure of their skills and it means you can do everyone ´s assessment all at once, like a regular test.
For example - a multichoice quiz. You ask a question or make a statement and the students must schoose from 3 or maybe 4 possible answers.
They would be doing this activity together and might enjoy the competition.
There is no need to make everything from scratch for the "quiz" test. Just take a regular test (computer file) and cut and paste-in the style and changes that you need.
If you, say, make it a 30 question "quiz", and then check answers every, say, 5 questions, it will feel like a quiz, even if they realise it is in fact a test.
Perhaps if it is your first day with this particular group, give small prizes for best scores etc.
What is the difference between a quiz and a test - only the stress that the students feel in my opinion.