Make it possible to use zope.testrunner.

You can do it like this:

  virtualenv .
  bin/pip install zope.testrunner zc.buildout
  bin/zope-testrunner --tests-pattern=test --test-path=.

setup.py

@@ -52,7 +52,7 @@
       ],
       extras_require={'buildout': ['zc.buildout']},
       tests_require=['zc.buildout'],
-      test_suite='z3c.checkversions.test.test',
+      test_suite='z3c.checkversions.test.test_suite',
       entry_points="""
       # -*- Entry points: -*-
       [console_scripts]

z3c/checkversions/test.py

@@ -21,7 +21,7 @@ def setUp(test):
 def tearDown(test):
     distutils.log.set_threshold(test._old_log_level)
 
-def test():
+def test_suite():
     optionflags = ELLIPSIS|NORMALIZE_WHITESPACE
     suite = DocFileSuite('README.txt', 'buildout.txt', 'installed.txt',
                          setUp=setUp, tearDown=tearDown,