How to add random test case in codewars?

I have function in codewars.com getNumberLength(n) which gets some number in different digits and should give you the length of number. For exampl number n=2000 shoul give 4. I also added some test cases with Test.assertEquals() method, but now I need to add test case with random numbers, does somebody know how to do that in codewars, because in their documentation I could not find explanation for random test case. They have their own test case methods, guys who have experience help please? For information function written in javascript.