diff --git a/sitewide/test/groupdetail_test.py b/sitewide/test/groupdetail_test.py
new file mode 100644
index 0000000..4440bb8
--- /dev/null
+++ b/sitewide/test/groupdetail_test.py
@@ -0,0 +1,146 @@
+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file or at
+# https://developers.google.com/open-source/licenses/bsd
+
+"""Unit test for User Group Detail servlet."""
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+
+import unittest
+
+from framework import exceptions
+from framework import permissions
+from services import service_manager
+from sitewide import groupdetail
+from testing import fake
+from testing import testing_helpers
+
+
+class GroupDetailTest(unittest.TestCase):
+  """Tests for the GroupDetail servlet."""
+
+  def setUp(self):
+    self.services = service_manager.Services(
+        project=fake.ProjectService(),
+        user=fake.UserService(),
+        usergroup=fake.UserGroupService())
+    self.services.user.TestAddUser('a@example.com', 111)
+    self.services.user.TestAddUser('b@example.com', 222)
+    self.services.user.TestAddUser('c@example.com', 333)
+    self.services.user.TestAddUser('group@example.com', 888)
+    self.services.usergroup.TestAddGroupSettings(888, 'group@example.com')
+    self.servlet = groupdetail.GroupDetail(
+        'req', 'res', services=self.services)
+    self.mr = testing_helpers.MakeMonorailRequest()
+    self.mr.viewed_username = 'group@example.com'
+    self.mr.viewed_user_auth.user_id = 888
+
+  def testAssertBasePermission(self):
+    mr = testing_helpers.MakeMonorailRequest(
+        perms=permissions.GetPermissions(None, {}, None))
+    mr.viewed_user_auth.user_id = 888
+    mr.auth.effective_ids = set([111])
+    self.assertRaises(
+        permissions.PermissionException,
+        self.servlet.AssertBasePermission, mr)
+    self.services.usergroup.TestAddMembers(888, [111], 'member')
+    self.servlet.AssertBasePermission(mr)
+
+  def testAssertBasePermission_IgnoreNoSuchGroup(self):
+    """The permission check does not crash for non-existent user groups."""
+    mr = testing_helpers.MakeMonorailRequest(
+        perms=permissions.GetPermissions(None, {}, None))
+    mr.viewed_user_auth.user_id = 404
+    mr.auth.effective_ids = set([111])
+    self.servlet.AssertBasePermission(mr)
+
+  def testAssertBasePermission_IndirectMembership(self):
+    self.services.usergroup.TestAddGroupSettings(999, 'subgroup@example.com')
+    mr = testing_helpers.MakeMonorailRequest(
+        perms=permissions.GetPermissions(None, {}, None))
+    mr.viewed_user_auth.user_id = 888
+    mr.auth.effective_ids = set([111])
+    self.assertRaises(
+        permissions.PermissionException,
+        self.servlet.AssertBasePermission, mr)
+    self.services.usergroup.TestAddMembers(888, [999], 'member')
+    self.services.usergroup.TestAddMembers(999, [111], 'member')
+    self.servlet.AssertBasePermission(mr)
+
+  def testGatherPagData_ZeroMembers(self):
+    page_data = self.servlet.GatherPageData(self.mr)
+    pagination = page_data['pagination']
+    self.assertEqual(0, len(pagination.visible_results))
+
+  def testGatherPagData_NonzeroMembers(self):
+    self.services.usergroup.TestAddMembers(888, [111, 222, 333])
+    page_data = self.servlet.GatherPageData(self.mr)
+    pagination = page_data['pagination']
+    self.assertEqual(3, len(pagination.visible_results))
+    self.assertEqual(3, pagination.total_count)
+    self.assertEqual(1, pagination.start)
+    self.assertEqual(3, pagination.last)
+    user_view_a, user_view_b, user_view_c = pagination.visible_results
+    self.assertEqual('a@example.com', user_view_a.email)
+    self.assertEqual('b@example.com', user_view_b.email)
+    self.assertEqual('c@example.com', user_view_c.email)
+
+  def testProcessAddMembers_NoneAdded(self):
+    post_data = fake.PostData(addmembers=[''], role=['member'])
+    url = self.servlet.ProcessAddMembers(self.mr, post_data)
+    self.assertIn('/g/group@example.com/?', url)
+    members_after, _ = self.services.usergroup.LookupMembers('cnxn', [888])
+    self.assertEqual(0, len(members_after[888]))
+
+    self.services.usergroup.TestAddMembers(888, [111, 222, 333])
+    url = self.servlet.ProcessAddMembers(self.mr, post_data)
+    self.assertIn('/g/group@example.com/?', url)
+    members_after, _ = self.services.usergroup.LookupMembers('cnxn', [888])
+    self.assertEqual(3, len(members_after[888]))
+
+  def testProcessAddMembers_SomeAdded(self):
+    self.services.usergroup.TestAddMembers(888, [111])
+    post_data = fake.PostData(
+        addmembers=['b@example.com, c@example.com'], role=['member'])
+    url = self.servlet.ProcessAddMembers(self.mr, post_data)
+    self.assertIn('/g/group@example.com/?', url)
+    members_after, _ = self.services.usergroup.LookupMembers('cnxn', [888])
+    self.assertEqual(3, len(members_after[888]))
+
+  def testProcessRemoveMembers_SomeRemoved(self):
+    self.services.usergroup.TestAddMembers(888, [111, 222, 333])
+    post_data = fake.PostData(remove=['b@example.com', 'c@example.com'])
+    url = self.servlet.ProcessRemoveMembers(self.mr, post_data)
+    self.assertIn('/g/group@example.com/?', url)
+    members_after, _ = self.services.usergroup.LookupMembers('cnxn', [888])
+    self.assertEqual(1, len(members_after[888]))
+
+  def testProcessFormData_NoPermission(self):
+    """Group members cannot edit group."""
+    self.services.usergroup.TestAddMembers(888, [111], 'member')
+    mr = testing_helpers.MakeMonorailRequest(
+        perms=permissions.GetPermissions(None, {}, None))
+    mr.viewed_user_auth.user_id = 888
+    mr.auth.effective_ids = set([111])
+    self.assertRaises(permissions.PermissionException,
+                      self.servlet.ProcessFormData, mr, {})
+
+  def testProcessFormData_OwnerPermission(self):
+    """Group owners cannot edit group."""
+    self.services.usergroup.TestAddMembers(888, [111], 'owner')
+    mr = testing_helpers.MakeMonorailRequest(
+        perms=permissions.GetPermissions(None, {}, None))
+    mr.viewed_user_auth.user_id = 888
+    mr.auth.effective_ids = set([111])
+    self.servlet.ProcessFormData(mr, {})
+
+  def testGatherPagData_NoSuchUserGroup(self):
+    """If there is no such user group, raise an exception."""
+    self.mr.viewed_user_auth.user_id = 404
+    self.assertRaises(
+        exceptions.NoSuchGroupException,
+        self.servlet.GatherPageData, self.mr)
+
+