Use 'zope-testrunner' within tox.

tox.ini

 [tox]
-envlist = py26,py27,py32,py33
+envlist = py26,py27,py32,py33,simple
 
 [testenv]
 commands =
-    python setup.py test -q
+# Run unit tests first.
+    zope-testrunner -u --test-path=src --auto-color --auto-progress
+# Only run functional tests if unit tests pass.
+    zope-testrunner -f -j99 --test-path=src --auto-color --auto-progress
 # without explicit deps, setup.py test will download a bunch of eggs into $PWD
 deps =
     BTrees
@@ -18,6 +21,14 @@ deps =
     zope.testing
     zope.testrunner
 
+[testenv:simple]
+# Test that 'setup.py test' works
+basepython =
+    python2.7
+commands =
+    python setup.py test -q
+deps = {[testenv]deps}
+
 [testenv:coverage]
 basepython =
     python2.7