Add missing test module docstring

Author: popescu-v

tests/test_dataset_class.py

@@ -4,6 +4,7 @@
 # which is available at https://spdx.org/licenses/BSD-3-Clause-Clear.html or         #
 # see the "LICENSE.md" file for more details.                                        #
 ######################################################################################
+"""Test the expected behavior of the Dataset class"""
 import os
 import shutil
 import unittest