fix importing of optional modules in auth_token

* keystone/middleware/auth_token.py: Catch the
correct exception so that the memcache and iso8601
modules can be optional as intended.
* tests/test_auth_token_middleware.py: Test
the ImportError path
* keystone/test.py: Add a new mixin class to
support disabling importing of a module.

Bug: 1003715
Change-Id: I87cc2f3bc79b17a52ea672bac7e0ebcf9e1fce57

3 files changed, 53 insertions, 7 deletions

diff --git a/keystone/middleware/auth_token.py b/keystone/middleware/auth_token.py
index a6f2af66..1551883d 100644
--- a/keystone/middleware/auth_token.py
+++ b/keystone/middleware/auth_token.py
@@ -161,7 +161,7 @@ class AuthProtocol(object):
                 LOG.info('Using memcache for caching token')
                 self._cache = memcache.Client(memcache_servers.split(','))
                 self._iso8601 = iso8601
-            except NameError as e:
+            except ImportError as e:
                 LOG.warn('disabled caching due to missing libraries %s', e)
 
     def __call__(self, env, start_response):
diff --git a/keystone/test.py b/keystone/test.py
index f968b4bb..54dc01b0 100644
--- a/keystone/test.py
+++ b/keystone/test.py
@@ -117,7 +117,45 @@ class TestClient(object):
         return self.request('PUT', path=path, headers=headers, body=body)
 
 
-class TestCase(unittest.TestCase):
+class NoModule(object):
+    """A mixin class to provide support for unloading/disabling modules."""
+
+    def __init__(self, *args, **kw):
+        super(NoModule, self).__init__(*args, **kw)
+        self._finders = []
+        self._cleared_modules = {}
+
+    def tearDown(self):
+        super(NoModule, self).tearDown()
+        for finder in self._finders:
+            sys.meta_path.remove(finder)
+        sys.modules.update(self._cleared_modules)
+
+    def clear_module(self, module):
+        cleared_modules = {}
+        for fullname in sys.modules.keys():
+            if fullname == module or fullname.startswith(module + '.'):
+                cleared_modules[fullname] = sys.modules.pop(fullname)
+        return cleared_modules
+
+    def disable_module(self, module):
+        """Ensure ImportError for the specified module."""
+
+        # Clear 'module' references in sys.modules
+        self._cleared_modules.update(self.clear_module(module))
+
+        # Disallow further imports of 'module'
+        class NoModule(object):
+            def find_module(self, fullname, path):
+                if fullname == module or fullname.startswith(module + '.'):
+                    raise ImportError
+
+        finder = NoModule()
+        self._finders.append(finder)
+        sys.meta_path.insert(0, finder)
+
+
+class TestCase(NoModule, unittest.TestCase):
     def __init__(self, *args, **kw):
         super(TestCase, self).__init__(*args, **kw)
         self._paths = []
@@ -243,8 +281,3 @@ class TestCase(unittest.TestCase):
     def add_path(self, path):
         sys.path.insert(0, path)
         self._paths.append(path)
-
-    def clear_module(self, module):
-        for x in sys.modules.keys():
-            if x.startswith(module):
-                del sys.modules[x]
diff --git a/tests/test_auth_token_middleware.py b/tests/test_auth_token_middleware.py
index 3ba1c57b..ccf7bba7 100644
--- a/tests/test_auth_token_middleware.py
+++ b/tests/test_auth_token_middleware.py
@@ -313,6 +313,19 @@ class AuthTokenMiddlewareTest(BaseAuthTokenMiddlewareTest):
         self.middleware(req.environ, self.start_fake_response)
         self.assertEqual(len(self.middleware._cache.set_value), 2)
 
+    def test_nomemcache(self):
+        self.disable_module('memcache')
+
+        conf = {
+            'admin_token': 'admin_token1',
+            'auth_host': 'keystone.example.com',
+            'auth_port': 1234,
+            'memcache_servers': 'localhost:11211',
+        }
+
+        auth_token.AuthProtocol(FakeApp(), conf)
+
+
 if __name__ == '__main__':
     import unittest
     unittest.main()