I appreciate the docstring, it's well written and clear.  My only suggestion would be relating future-maintenance.  It's good to have documentation near-by the implementation, that way if code changes, docs easy to find and remember to update.   So for the main docstring, you can keep it simple like:

     1. Run some containers with different memory values via parameter -m
     2. Check if the container start or not as expected by sub-subtest

Then in the sub-subtest classes, put their specific documentation, like:

    class memory_positive(run_memory_base):

        """"
        Pass a random number which in the valid range and all the 
        unit options, '', '0', 'b', 'B', 'k', 'K', 'm', 'M', 'g','G'.Then check if the
        cgroup resource memory.limit_in_bytes match the memory,
        fail if both container start failed and memory mismatch its cgroup 
        resource.
        """"

Also because (someday) we will auto-generate documentation from these docstrings, so having it matched to the class will be helpful :grinning: