Require test deps explicitly in tox.ini.

I think, the term "z3c.testsetup[test]" in tox.ini deps
tells tox to fetch an (old) "z3c.testsetup" package from pypi
and then read the "test" dependencies from this package. It does
not (as one might expect) read the "test" dependencies from the
locally developed setup.py file.

setup.py

@@ -5,6 +5,7 @@ def read(*rnames):
     return open(os.path.join(os.path.dirname(__file__), *rnames)).read()
 
 tests_require = [
+    # please also add all test requirements to tox.ini.
     'zope.app.testing',
     'zope.app.zcmlfiles',
     'zope.component',

tox.ini

@@ -6,6 +6,8 @@ envlist =
 usedevelop = true
 deps =
     zope.testrunner
-    z3c.testsetup[test]
+    zope.app.testing
+    zope.app.zcmlfiles
+    zope.component
 commands =
     zope-testrunner --test-path=src --tests-pattern='^test_.*$' {posargs:-v}