remove usage of evil / broken unittest.mock, use mock from pypi

see testsuite.mock docstring for more details.

one test shows brokenness right now that was hidden / silent until now.

borg/testsuite/mock.py

@@ -1,5 +1,14 @@
-try:
-    # Only available in python 3.3+
-    from unittest.mock import *
-except ImportError:
-    from mock import *
+"""
+Mocking
+
+Note: unittest.mock is broken on at least python 3.3.6 and 3.4.0.
+      it silently ignores mistyped method names starting with assert_...,
+      does nothing and just succeeds.
+      The issue was fixed in the separately distributed "mock" lib, you
+      get an AttributeError there. So, always use that one!
+
+Details:
+
+http://engineeringblog.yelp.com/2015/02/assert_called_once-threat-or-menace.html
+"""
+from mock import *

borg/testsuite/repository.py

@@ -159,7 +159,7 @@ class RepositoryCommitTestCase(RepositoryTestCaseBase):
         with patch.object(UpgradableLock, 'upgrade', side_effect=UpgradableLock.WriteLockFailed) as upgrade:
             self.reopen()
             self.assert_raises(UpgradableLock.WriteLockFailed, lambda: len(self.repository))
-            upgrade.assert_called_once()
+            upgrade.assert_called_once_with()
 
     def test_crash_before_write_index(self):
         self.add_keys()
@@ -309,7 +309,7 @@ class RepositoryCheckTestCase(RepositoryTestCaseBase):
         # Simulate a crash before compact
         with patch.object(Repository, 'compact_segments') as compact:
             self.repository.commit()
-            compact.assert_called_once()
+            compact.assert_called_once_with()
         self.reopen()
         self.check(repair=True)
         self.assert_equal(self.repository.get(bytes(32)), b'data2')

tox.ini

@@ -6,10 +6,6 @@ envlist = py32, py33, py34
 changedir = {envdir}
 deps =
     pytest
+    mock
 commands = py.test
 passenv = *  # fakeroot -u needs some env vars
-
-[testenv:py32]
-deps =
-    pytest
-    mock