Tests work without the backport of mock.

src/gevent/testing/__init__.py

@@ -128,9 +128,20 @@ def gc_collect_if_needed():
     if PYPY: # pragma: no cover
         gc.collect()
 
+# Our usage of mock should be limited to '@mock.patch()'
+# and other things that are easily...mocked...here on Python 2
+# when mock is not installed.
 try:
     from unittest import mock
 except ImportError: # Python 2
+    try:
         import mock
+    except ImportError: # pragma: no cover
+        # Backport not installed
+        class mock(object):
+
+            @staticmethod
+            def patch(reason):
+                return unittest.skip(reason)
 
 mock = mock

src/gevent/testing/leakcheck.py

@@ -27,7 +27,7 @@ import unittest
 
 try:
     import objgraph
-except ImportError:
+except ImportError: # pragma: no cover
     # Optional test dependency
     objgraph = None