Indiana University has a variety of creativity tests that are well-explained and at least some are suitable for ESL teachers, from an English teaching standpoint as well as for the actual measuring of creativity*.
The first test I looked at is the Guilford's Alternative uses task. It is simple and easy to understand grade.
The test (and there may be a time limit- I think you merely need this if you are testing a class - keep all of them bound by the same limit. See my disclaimer (*) below) is simple: "Name all the uses for a brick".
There are four components to scoring the test and the final one looks useful for ESL instructors:
Elaboration - amount of detail (for Example "a doorstop" = 0 whereas "a door stop to prevent a door slamming shut in a strong wind" = 2 (one for explanation of door slamming, two for further detail about the wind).The next one is a little tricky. There appear to be several forms of the Torrance Tests of Creative Thinking (Indiana University, Newsweek). Both forms that I looked at displayed a few lines on a page and either asked students to describe what they were looking at -ala a Roschart test, or to add to the lines and complete the drawing. However it is done, it appears interesting although there is relatively little English used. I guess a teacher could have a student complete the drawing, then describe it, but that, while reasonable, is merely appending the ESL component to the test. This test appears to require training to properly use it, but as a conversation starter, it would seem to be useful to lay-personel.
From Indiana U:
To score the TTCT you will need "Manual for Scoring and Interpreting Results", obtainable from the Torrance Center, or from Scholastic Testing Service. The manual includes national norms, standard scores, and national percentiles for each age level.
Other tests look at creative problem solving and resemble 'Lateral Thinking exercises". One example from Indiana U goes like this.
"Marsha and Marjorie were born on the same day of the same month of the same year to the same mother and the same father yet they are not twins. How is that possible?"
The first test I describe above specifically says "no training required", but I am leery of this. I am by no means a psychologist nor do I feel confident in rating people's abilities in anything aside from ESL and competitive swimming (I was a competitor for many years and a coach for many more years afterward).