Add the debug flag to tox.ini

Allows us to set a breakpoint in code, using pdb.set_trace().
Documentation on how to debug has also been added.
Change-Id: I34bde581ce331b2eb63e4dab08e9f9c597598bf1

doc/source/testing.rst

@@ -83,6 +83,21 @@ the functional tests through tox.
 By default, the functional tox job will use ``testr`` to execute the
 functional tests.
 
+Debugging
+---------
+
+In order to be able to debug code in Castellan, you must use the Python
+Debugger. This can be done by adding ``import pdb; pdb.set_trace()``
+to set the breakpoint. Then run the following command to hit the breakpoint:
+
+.. code-block:: bash
+
+    # hit the pdb breakpoint
+    tox -e debug
+
+Once in the Python Debugger, you can use the commands as stated in the
+`Debugger Commands` section here: https://docs.python.org/2/library/pdb.html
+
 Pep8 Check
 ----------
 

tox.ini

@@ -19,6 +19,9 @@ commands = flake8
 [testenv:venv]
 commands = {posargs}
 
+[testenv:debug]
+commands = oslo_debug_helper {posargs}
+
 [testenv:cover]
 commands = python setup.py testr --coverage --testr-args='{posargs}'