Add support to use pdb with tox

TrivialFix

Change-Id: I6f32ce7033fe5a8b8f628a8f52dde67b9540083d

doc/running-tests.rst

@@ -82,7 +82,25 @@ the ``kolla/tests/test_kolla_docker.py``` file:
 
     $ tox -e py27 test_kolla_docker.ModuleArgsTest.test_module_args
 
+Debugging unit tests
+------------------------
+
+In order to break into the debugger from a unit test we need to insert
+a breaking point to the code:
+
+.. code-block:: python
+
+  import pdb; pdb.set_trace()
+
+Then run ``tox`` with the debug environment as one of the following::
+
+  tox -e debug
+  tox -e debug test_file_name.TestClass.test_name
+
+For more information see the `oslotest documentation
+<http://docs.openstack.org/developer/oslotest/features.html#debugging-with-oslo-debug-helper>`_.
+
 
 .. rubric:: Footnotes
 
-.. [#f1] See http://docs.openstack.org/infra/system-config/jenkins.html
+.. [#f1] See http://docs.openstack.org/infra/system-config/jenkins.html
\ No newline at end of file

tox.ini

@@ -17,6 +17,9 @@ commands =
   find . -type f -name "*.pyc" -delete
   python setup.py test --slowest --testr-args='{posargs}'
 
+[testenv:debug]
+commands = oslo_debug_helper {posargs}
+
 [testenv:pep8]
 commands =
   {toxinidir}/tools/run-bashate.sh