dev-python/zc-buildout: Partially enable tests

Add missing test dependencies and python_test() implementation. Sadly,
the tests fail hard with Python 3.

dev-python/zc-buildout/zc-buildout-2.5.3.ebuild

@@ -1,4 +1,4 @@
-# Copyright 1999-2016 Gentoo Foundation
+# Copyright 1999-2017 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=5
@@ -16,18 +16,28 @@ SRC_URI="mirror://pypi/${MY_PN:0:1}/${MY_PN}/${MY_P}.tar.gz"
 LICENSE="ZPL"
 SLOT="0"
 KEYWORDS="~amd64 ~x86"
-IUSE=""
+IUSE="test"
 
 RDEPEND=">=dev-python/setuptools-3.3[${PYTHON_USEDEP}]"
-DEPEND="${RDEPEND}"
+DEPEND="${RDEPEND}
+	test? ( dev-python/zope-testing[${PYTHON_USEDEP}] )"
 
 S="${WORKDIR}"/${MY_P}
 
 DOCS=( README.rst doc/tutorial.txt )
-# Tests require zope packages absent from portage
 
 # Prevent incorrect installation of data file
 python_prepare_all() {
 	sed -e '/^    include_package_data/d' -i setup.py || die
 	distutils-r1_python_prepare_all
 }
+
+python_test() {
+	if python_is_python3; then
+		ewarn "Tests are broken for ${EPYTHON}, skipping"
+		continue
+	fi
+
+	distutils_install_for_testing
+	"${PYTHON}" src/zc/buildout/tests.py || die "Tests fail with ${EPYTHON}"
+}