Ignore ResourceWarnings in various modules in a 2-compatible way.

Sometimes tests are flaky about giving this warning, particularly in ACME. I recommend just ignoring them.

acme/acme/crypto_util_test.py

@@ -16,8 +16,9 @@ from acme import errors
 from acme import test_util
 from acme.magic_typing import List # pylint: disable=unused-import, no-name-in-module
 
-# turns all warnings into errors for this module
-pytestmark = pytest.mark.filterwarnings("ignore::ResourceWarning")
+# turns all ResourceWarnings into errors for this module
+if six.PY3:
+    pytestmark = pytest.mark.filterwarnings("ignore::ResourceWarning")
 
 
 class SSLSocketAndProbeSNITest(unittest.TestCase):

acme/acme/messages_test.py

@@ -4,6 +4,7 @@ import unittest
 import josepy as jose
 import mock
 import pytest
+import six
 
 from acme import challenges
 from acme import test_util
@@ -14,6 +15,10 @@ CERT = test_util.load_comparable_cert('cert.der')
 CSR = test_util.load_comparable_csr('csr.der')
 KEY = test_util.load_rsa_private_key('rsa512_key.pem')
 
+# turns all ResourceWarnings into errors for this module
+if six.PY3:
+    pytestmark = pytest.mark.filterwarnings("ignore::ResourceWarning")
+
 
 class ErrorTest(unittest.TestCase):
     """Tests for acme.messages.Error."""
@@ -167,7 +172,6 @@ class DirectoryTest(unittest.TestCase):
         from acme.messages import Directory
         Directory.from_json({'foo': 'bar'})
 
-    @pytest.mark.filterwarnings("ignore::ResourceWarning")
     def test_iter_meta(self):
         result = False
         for k in self.dir.meta:

acme/acme/standalone_test.py

@@ -6,6 +6,7 @@ import threading
 import tempfile
 import unittest
 
+import six
 from six.moves import http_client  # pylint: disable=import-error
 from six.moves import queue  # pylint: disable=import-error
 from six.moves import socketserver  # type: ignore  # pylint: disable=import-error
@@ -20,8 +21,9 @@ from acme import crypto_util
 from acme import test_util
 from acme.magic_typing import Set # pylint: disable=unused-import, no-name-in-module
 
-# turns all warnings into errors for this module
-pytestmark = pytest.mark.filterwarnings("ignore::ResourceWarning")
+# turns all ResourceWarnings into errors for this module
+if six.PY3:
+    pytestmark = pytest.mark.filterwarnings("ignore::ResourceWarning")
 
 
 class TLSServerTest(unittest.TestCase):

acme/acme/util_test.py

@@ -1,6 +1,13 @@
 """Tests for acme.util."""
 import unittest
 
+import pytest
+import six
+
+# turns all ResourceWarnings into errors for this module
+if six.PY3:
+    pytestmark = pytest.mark.filterwarnings("ignore::ResourceWarning")
+
 
 class MapKeysTest(unittest.TestCase):
     """Tests for acme.util.map_keys."""