Debug env for tox

Running a test with pdb was difficult because tox captures
output and causes pdb prompt to quit.

Tips for how to run with debug are provided here:
 https://wiki.openstack.org/wiki/Testr#Debugging_.28pdb.29_Tests

This change puts these commands into a debug env in tox.ini so
you can do a command like:

tox -e debug pycadf.tests.test_cadf_spec

and when it hits your breakpoint you'll get the debug prompt.

Change-Id: Ic53a888e4e305d51159d1d6a2f962786a532e089
Co-Authored-By: Brant Knudson <bknudson@us.ibm.com>
Closes-Bug: #1350424

doc/source/contributing/source.rst

@@ -68,12 +68,14 @@ run through tox_.
 
       $ tox -e py27 -- api.v2
 
-   To debug tests (ie. break into pdb debugger), you can use ''venv'' command::
+   To debug tests (ie. break into pdb debugger), you can use ''debug'' tox
+   environment. Here's an example, passing the name of a test since you'll
+   normally only want to run the test that hits your breakpoint::
 
-      $ tox -e venv "python -m unittest discover ceilometer"
+       $ tox -e debug ceilometer.tests.test_bin
 
-   Unfortunately, debugging currently has some limitations:
-   You cannot run a specific test, you have to launch the whole test suite.
+   For reference, the ``debug`` tox environment implements the instructions
+   here: https://wiki.openstack.org/wiki/Testr#Debugging_.28pdb.29_Tests
 
 .. seealso::
 

tools/debug_helper.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+
+TMP_DIR=`mktemp -d` || exit 1
+trap "rm -rf $TMP_DIR" EXIT
+
+ALL_TESTS=$TMP_DIR/all_tests
+TESTS_TO_RUN=$TMP_DIR/ks_to_run
+
+python -m testtools.run discover -t ./ ./ceilometer/tests --list > $ALL_TESTS
+
+if [ "$1" ]; then
+    grep "$1" < $ALL_TESTS > $TESTS_TO_RUN
+else
+    mv $ALL_TESTS $TESTS_TO_RUN
+fi
+
+STANDARD_THREADS=1 python -m testtools.run discover --load-list $TESTS_TO_RUN

tox.ini

@@ -44,6 +44,10 @@ commands = python setup.py build_sphinx
 [testenv:venv]
 commands = {posargs}
 
+[testenv:debug]
+commands =
+   bash -x {toxinidir}/setup-test-env.sh {toxinidir}/tools/debug_helper.sh {posargs}
+
 [flake8]
 # H305 imports not grouped correctly
 ignore = H305