Remember, the Test Suite is a MATLAB script which, in turn, calls and/or parses the students' code function. So my first recommendation is to use MATLAB on your desktop to build, debug and test your script.
Online, you can also use "Run Tests" during problem creation. Command output is echoed, thus you can print diagnostic data if desired. You can also experiment with MATLAB commands such as dir(), path(), which() etc. as needed.
As a last resort, the host system within which your Test Suite and students' function MATLAB code is executed runs linux. You can use the MATLAB shell escape (!, exclamation point) to execute any needed server-side shell commands. For example, !ls will list all files in the current working directory.
There are many possibilities the power of the MATLAB language offers for implementing test suites. We will add more information and examples in future, and I encourage you to share your own insights as answers or comments below.