diff --git a/tests/test_oauth2client_gce.py b/tests/test_oauth2client_gce.py
new file mode 100644
index 0000000..15e45c4
--- /dev/null
+++ b/tests/test_oauth2client_gce.py
@@ -0,0 +1,92 @@
+# Copyright 2012 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+"""Tests for oauth2client.gce.
+
+Unit tests for oauth2client.gce.
+"""
+
+__author__ = 'jcgregorio@google.com (Joe Gregorio)'
+
+import unittest
+import mox
+
+from oauth2client.client import AccessTokenRefreshError
+from oauth2client.client import Credentials
+from oauth2client.gce import AppAssertionCredentials
+
+
+class AssertionCredentialsTests(unittest.TestCase):
+
+  def test_good_refresh(self):
+    m = mox.Mox()
+
+    httplib2_response = m.CreateMock(object)
+    httplib2_response.status = 200
+
+    httplib2_request = m.CreateMock(object)
+    httplib2_request.__call__(
+        ('http://metadata.google.internal/0.1/meta-data/service-accounts/'
+         'default/acquire'
+         '?scope=http%3A%2F%2Fexample.com%2Fa%20http%3A%2F%2Fexample.com%2Fb'
+        )).AndReturn((httplib2_response, '{"accessToken": "this-is-a-token"}'))
+
+    m.ReplayAll()
+
+    c = AppAssertionCredentials(scope=['http://example.com/a',
+                                       'http://example.com/b'])
+
+    c._refresh(httplib2_request)
+
+    self.assertEquals('this-is-a-token', c.access_token)
+
+    m.UnsetStubs()
+    m.VerifyAll()
+
+
+  def test_fail_refresh(self):
+    m = mox.Mox()
+
+    httplib2_response = m.CreateMock(object)
+    httplib2_response.status = 400
+
+    httplib2_request = m.CreateMock(object)
+    httplib2_request.__call__(
+        ('http://metadata.google.internal/0.1/meta-data/service-accounts/'
+         'default/acquire'
+         '?scope=http%3A%2F%2Fexample.com%2Fa%20http%3A%2F%2Fexample.com%2Fb'
+        )).AndReturn((httplib2_response, '{"accessToken": "this-is-a-token"}'))
+
+    m.ReplayAll()
+
+    c = AppAssertionCredentials(scope=['http://example.com/a',
+                                       'http://example.com/b'])
+
+    try:
+      c._refresh(httplib2_request)
+      self.fail('Should have raised exception on 400')
+    except AccessTokenRefreshError:
+      pass
+
+    m.UnsetStubs()
+    m.VerifyAll()
+
+  def test_to_from_json(self):
+    c = AppAssertionCredentials(scope=['http://example.com/a',
+                                       'http://example.com/b'])
+    json = c.to_json()
+    c2 = Credentials.new_from_json(json)
+
+    self.assertEqual(c.access_token, c2.access_token)