Mark Py 2/3-only tests as skip instead of xfail

Also reuse pre-defined py2_only and py3_only decorators where
appropriate.

setuptools/tests/test_build_meta.py

@@ -7,6 +7,7 @@ import pytest
 
 from .files import build_files
 from .textwrap import DALS
+from . import py2_only
 
 __metaclass__ = type
 
@@ -143,7 +144,7 @@ def test_prepare_metadata_for_build_wheel(build_backend):
     assert os.path.isfile(os.path.join(dist_dir, dist_info, 'METADATA'))
 
 
-@pytest.mark.skipif('sys.version_info > (3,)')
+@py2_only
 def test_prepare_metadata_for_build_wheel_with_str(build_backend):
     dist_dir = os.path.abspath(str('pip-dist-info'))
     os.makedirs(dist_dir)

setuptools/tests/test_manifest.py

@@ -15,13 +15,12 @@ from setuptools.command.egg_info import FileList, egg_info, translate_pattern
 from setuptools.dist import Distribution
 from setuptools.extern import six
 from setuptools.tests.textwrap import DALS
+from . import py3_only
 
 import pytest
 
 __metaclass__ = type
 
-py3_only = pytest.mark.xfail(six.PY2, reason="Test runs on Python 3 only")
-
 
 def make_local_path(s):
     """Converts '/' in a string to os.sep"""

setuptools/tests/test_namespaces.py

@@ -12,7 +12,7 @@ from setuptools.command import test
 
 class TestNamespaces:
 
-    @pytest.mark.xfail(
+    @pytest.mark.skipif(
         sys.version_info < (3, 5),
         reason="Requires importlib.util.module_from_spec",
     )

setuptools/tests/test_sdist.py

@@ -20,8 +20,8 @@ from setuptools.command.egg_info import manifest_maker
 from setuptools.dist import Distribution
 from setuptools.tests import fail_on_ascii
 from .text import Filenames
+from . import py3_only
 
-py3_only = pytest.mark.xfail(six.PY2, reason="Test runs on Python 3 only")
 
 SETUP_ATTRS = {
     'name': 'sdist_test',

setuptools/tests/test_test.py

@@ -93,7 +93,7 @@ def test_test(capfd):
     assert out == 'Foo\n'
 
 
-@pytest.mark.xfail(
+@pytest.mark.skipif(
     sys.version_info < (2, 7),
     reason="No discover support for unittest on Python 2.6",
 )