You can use `multiprocessing` module in any function/class called from TestStand's Python adapter. Before creating instance of `Process`, you need to use `multiprocessing.set_executable` by pointing to the python exe you want to use for multiprocess.
Reason: TestStand executes Python modules in an external process which embeds CPython interpreter. By default, `multiprocessing` module uses `sys.executable` which will be the path of current executable (which is the process shipped along with TestStand). TestStand's executable is designed to work only when called from TestStand. If using `multiprocessing` module, you will be calling TestStand's executable from Python which does not work since the parameters are not understood by the exe. Hence, in your code, explicitly mention the Python executable to be used for multiprocessing.
Note: We do have plans to for improving the behavior where multiprocessing works out of the box.