diff --git a/letsencrypt/client/le_util.py b/letsencrypt/client/le_util.py
index 75924e08b..42f88bc5d 100644
--- a/letsencrypt/client/le_util.py
+++ b/letsencrypt/client/le_util.py
@@ -17,6 +17,10 @@ def make_or_verify_dir(directory, mode=0o755, uid=0):
     :raises LetsEncryptClientError: if a directory already exists,
         but has wrong permissions or owner
 
+    :raises OSError: if invalid or inaccessible file names and
+        paths, or other arguments that have the correct type,
+        but are not accepted by the operating system.
+
     """
     try:
         os.makedirs(directory, mode)
diff --git a/letsencrypt/client/tests/le_util_test.py b/letsencrypt/client/tests/le_util_test.py
index 926830602..2432a6d65 100644
--- a/letsencrypt/client/tests/le_util_test.py
+++ b/letsencrypt/client/tests/le_util_test.py
@@ -4,6 +4,8 @@ import shutil
 import tempfile
 import unittest
 
+import mock
+
 
 class MakeOrVerifyDirTest(unittest.TestCase):
     """Tests for letsencrypt.client.le_util.make_or_verify_dir.
@@ -40,6 +42,11 @@ class MakeOrVerifyDirTest(unittest.TestCase):
     def test_existing_wrong_mode_fails(self):
         self.assertRaises(Exception, self._call, self.path, 0o600)
 
+    def test_reraises_os_error(self):
+        with mock.patch.object(os, 'makedirs') as makedirs:
+            makedirs.side_effect = OSError()
+            self.assertRaises(OSError, self._call, 'bar', 12312312)
+
 
 class CheckPermissionsTest(unittest.TestCase):
     """Tests for letsencrypt.client.le_util.check_permissions.
@@ -69,6 +76,49 @@ class CheckPermissionsTest(unittest.TestCase):
         self.assertFalse(self._call(0o600))
 
 
+class UniqueFileTest(unittest.TestCase):
+    """Tests for letsencrypt.class.le_util.unique_file."""
+
+    def setUp(self):
+        self.root_path = tempfile.mkdtemp()
+        self.default_name = os.path.join(self.root_path, 'foo.txt')
+
+    def _call(self, mode=0o600):
+        from letsencrypt.client.le_util import unique_file
+        return unique_file(self.default_name, mode)
+
+    def test_returns_fd_for_writing(self):
+        fd, name = self._call()
+        fd.write('bar')
+        fd.close()
+        self.assertEqual(open(name).read(), 'bar')
+
+    def test_right_mode(self):
+        self.assertEqual(0o700, os.stat(self._call(0o700)[1]).st_mode & 0o777)
+        self.assertEqual(0o100, os.stat(self._call(0o100)[1]).st_mode & 0o777)
+
+    def test_default_not_exists(self):
+        self.assertEqual(self._call()[1], self.default_name)
+
+    def test_default_exists(self):
+        name1 = self._call()[1]  # create foo.txt
+        name2 = self._call()[1]
+        name3 = self._call()[1]
+
+        self.assertNotEqual(name1, name2)
+        basename2 = os.path.basename(name2)
+        self.assertEqual(os.path.dirname(name2), self.root_path)
+        self.assertTrue(basename2.startswith('foo'))
+        self.assertTrue(basename2.endswith('.txt'))
+
+        self.assertNotEqual(name1, name3)
+        self.assertNotEqual(name2, name3)
+        basename3 = os.path.basename(name3)
+        self.assertEqual(os.path.dirname(name3), self.root_path)
+        self.assertTrue(basename3.startswith('foo'))
+        self.assertTrue(basename3.endswith('.txt'))
+
+
 # https://en.wikipedia.org/wiki/Base64#Examples
 JOSE_B64_PADDING_EXAMPLES = {
     'any carnal pleasure.': ('YW55IGNhcm5hbCBwbGVhc3VyZS4', '='),
@@ -129,6 +179,9 @@ class JOSEB64DecodeTest(unittest.TestCase):
     def test_non_ascii_unicode_fails(self):
         self.assertRaises(ValueError, self._call, u'\u0105')
 
+    def test_type_error_no_unicode_or_str(self):
+        self.assertRaises(TypeError, self._call, object())
+
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/setup.py b/setup.py
index a80a22778..462759c1c 100755
--- a/setup.py
+++ b/setup.py
@@ -6,6 +6,7 @@ install_requires = [
     'argparse',
     'jsonschema',
     'M2Crypto',
+    'mock',
     'pycrypto',
     'python-augeas',
     'python2-pythondialog',
@@ -21,7 +22,7 @@ testing_extras = [
     'mock',
     'nose',
     'nosexcover',
-    'pylint',
+    'pylint<1.4',  # py2.6 compat, c.f #97
     'tox',
 ]