diff --git a/search/test/frontendsearchpipeline_test.py b/search/test/frontendsearchpipeline_test.py
new file mode 100644
index 0000000..b2e7fb3
--- /dev/null
+++ b/search/test/frontendsearchpipeline_test.py
@@ -0,0 +1,1339 @@
+# 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
+
+"""Tests for the frontendsearchpipeline module."""
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+
+import mox
+import unittest
+
+from google.appengine.api import memcache
+from google.appengine.api import modules
+from google.appengine.ext import testbed
+from google.appengine.api import urlfetch
+
+import settings
+from framework import framework_helpers
+from framework import sorting
+from framework import urls
+from proto import ast_pb2
+from proto import project_pb2
+from proto import tracker_pb2
+from search import frontendsearchpipeline
+from search import searchpipeline
+from search import query2ast
+from services import service_manager
+from testing import fake
+from testing import testing_helpers
+from tracker import tracker_bizobj
+
+
+# Just an example timestamp.  The value does not matter.
+NOW = 2444950132
+
+
+class FrontendSearchPipelineTest(unittest.TestCase):
+
+  def setUp(self):
+    self.config = tracker_bizobj.MakeDefaultProjectIssueConfig(789)
+    self.services = service_manager.Services(
+        user=fake.UserService(),
+        project=fake.ProjectService(),
+        issue=fake.IssueService(),
+        config=fake.ConfigService(),
+        cache_manager=fake.CacheManager())
+    self.services.user.TestAddUser('a@example.com', 111)
+    self.project = self.services.project.TestAddProject('proj', project_id=789)
+    self.mr = testing_helpers.MakeMonorailRequest(
+      path='/p/proj/issues/list', project=self.project)
+    self.mr.me_user_id = 111
+
+    self.issue_1 = fake.MakeTestIssue(
+      789, 1, 'one', 'New', 111, labels=['Priority-High'])
+    self.services.issue.TestAddIssue(self.issue_1)
+    self.issue_2 = fake.MakeTestIssue(
+      789, 2, 'two', 'New', 111, labels=['Priority-Low'])
+    self.services.issue.TestAddIssue(self.issue_2)
+    self.issue_3 = fake.MakeTestIssue(
+      789, 3, 'three', 'New', 111, labels=['Priority-Medium'])
+    self.services.issue.TestAddIssue(self.issue_3)
+    self.mr.sort_spec = 'Priority'
+
+    self.cnxn = self.mr.cnxn
+    self.project = self.mr.project
+    self.auth = self.mr.auth
+    self.me_user_id = self.mr.me_user_id
+    self.query = self.mr.query
+    self.query_project_names = self.mr.query_project_names
+    self.items_per_page = self.mr.num # defaults to 100
+    self.paginate_start = self.mr.start
+    self.paginate_end = self.paginate_start + self.items_per_page
+    self.can = self.mr.can
+    self.group_by_spec = self.mr.group_by_spec
+    self.sort_spec = self.mr.sort_spec
+    self.warnings = self.mr.warnings
+    self.errors = self.mr.errors
+    self.use_cached_searches = self.mr.use_cached_searches
+    self.profiler = self.mr.profiler
+
+    self.mox = mox.Mox()
+    self.testbed = testbed.Testbed()
+    self.testbed.activate()
+    self.testbed.init_user_stub()
+    self.testbed.init_memcache_stub()
+    sorting.InitializeArtValues(self.services)
+
+  def tearDown(self):
+    self.testbed.deactivate()
+    self.mox.UnsetStubs()
+    self.mox.ResetAll()
+
+  def testSearchForIIDs_AllResultsCached_AllAtRiskCached(self):
+    unfiltered_iids = {(1, 'p:v'): [1001, 1011]}
+    nonviewable_iids = {1: set()}
+    self.mox.StubOutWithMock(frontendsearchpipeline, '_StartBackendSearch')
+    frontendsearchpipeline._StartBackendSearch(
+        self.cnxn, ['proj'], [789], mox.IsA(tracker_pb2.ProjectIssueConfig),
+        unfiltered_iids, {}, nonviewable_iids, set(), self.services,
+        self.me_user_id, self.auth.user_id or 0, self.paginate_end,
+        self.query.split(' OR '), self.can, self.group_by_spec, self.sort_spec,
+        self.warnings, self.use_cached_searches).AndReturn([])
+    self.mox.StubOutWithMock(frontendsearchpipeline, '_FinishBackendSearch')
+    frontendsearchpipeline._FinishBackendSearch([])
+    self.mox.ReplayAll()
+
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+    pipeline.unfiltered_iids = unfiltered_iids
+    pipeline.nonviewable_iids = nonviewable_iids
+    pipeline.SearchForIIDs()
+    self.mox.VerifyAll()
+    self.assertEqual(2, pipeline.total_count)
+    self.assertEqual([1001, 1011], pipeline.filtered_iids[(1, 'p:v')])
+
+  def testSearchForIIDs_CrossProject_AllViewable(self):
+    self.services.project.TestAddProject('other', project_id=790)
+    unfiltered_iids = {(1, 'p:v'): [1001, 1011, 2001]}
+    nonviewable_iids = {1: set()}
+    self.query_project_names = ['other']
+    self.mox.StubOutWithMock(frontendsearchpipeline, '_StartBackendSearch')
+    frontendsearchpipeline._StartBackendSearch(
+        self.cnxn, ['other', 'proj'], [789, 790],
+        mox.IsA(tracker_pb2.ProjectIssueConfig), unfiltered_iids, {},
+        nonviewable_iids, set(), self.services,
+        self.me_user_id, self.auth.user_id or 0, self.paginate_end,
+        self.query.split(' OR '), self.can, self.group_by_spec, self.sort_spec,
+        self.warnings, self.use_cached_searches).AndReturn([])
+    self.mox.StubOutWithMock(frontendsearchpipeline, '_FinishBackendSearch')
+    frontendsearchpipeline._FinishBackendSearch([])
+    self.mox.ReplayAll()
+
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+
+    pipeline.unfiltered_iids = unfiltered_iids
+    pipeline.nonviewable_iids = nonviewable_iids
+    pipeline.SearchForIIDs()
+    self.mox.VerifyAll()
+    self.assertEqual(3, pipeline.total_count)
+    self.assertEqual([1001, 1011, 2001], pipeline.filtered_iids[(1, 'p:v')])
+
+  def testSearchForIIDs_CrossProject_MembersOnlyOmitted(self):
+    self.services.project.TestAddProject(
+        'other', project_id=790, access=project_pb2.ProjectAccess.MEMBERS_ONLY)
+    unfiltered_iids = {(1, 'p:v'): [1001, 1011]}
+    nonviewable_iids = {1: set()}
+    # project 'other' gets filtered out before the backend call.
+    self.mr.query_project_names = ['other']
+    self.mox.StubOutWithMock(frontendsearchpipeline, '_StartBackendSearch')
+    frontendsearchpipeline._StartBackendSearch(
+        self.cnxn, ['proj'], [789], mox.IsA(tracker_pb2.ProjectIssueConfig),
+        unfiltered_iids, {}, nonviewable_iids, set(), self.services,
+        self.me_user_id, self.auth.user_id or 0, self.paginate_end,
+        self.query.split(' OR '), self.can, self.group_by_spec, self.sort_spec,
+        self.warnings, self.use_cached_searches).AndReturn([])
+    self.mox.StubOutWithMock(frontendsearchpipeline, '_FinishBackendSearch')
+    frontendsearchpipeline._FinishBackendSearch([])
+    self.mox.ReplayAll()
+
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+    pipeline.unfiltered_iids = unfiltered_iids
+    pipeline.nonviewable_iids = nonviewable_iids
+    pipeline.SearchForIIDs()
+    self.mox.VerifyAll()
+    self.assertEqual(2, pipeline.total_count)
+    self.assertEqual([1001, 1011], pipeline.filtered_iids[(1, 'p:v')])
+
+  def testMergeAndSortIssues_EmptyResult(self):
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+    pipeline.filtered_iids = {0: [], 1: [], 2: []}
+
+    pipeline.MergeAndSortIssues()
+    self.assertEqual([], pipeline.allowed_iids)
+    self.assertEqual([], pipeline.allowed_results)
+    self.assertEqual({}, pipeline.users_by_id)
+
+  def testMergeAndSortIssues_Normal(self):
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+    # In this unit test case we are not calling SearchForIIDs(), instead just
+    # set pipeline.filtered_iids directly.
+    pipeline.filtered_iids = {
+      0: [],
+      1: [self.issue_1.issue_id],
+      2: [self.issue_2.issue_id],
+      3: [self.issue_3.issue_id]
+      }
+
+    pipeline.MergeAndSortIssues()
+    self.assertEqual(
+      [self.issue_1.issue_id, self.issue_2.issue_id, self.issue_3.issue_id],
+      pipeline.allowed_iids)
+    self.assertEqual(
+      [self.issue_1, self.issue_3, self.issue_2],  # high, medium, low.
+      pipeline.allowed_results)
+    self.assertEqual([0, 111], list(pipeline.users_by_id.keys()))
+
+  def testDetermineIssuePosition_Normal(self):
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+    # In this unit test case we are not calling SearchForIIDs(), instead just
+    # set pipeline.filtered_iids directly.
+    pipeline.filtered_iids = {
+      0: [],
+      1: [self.issue_1.issue_id],
+      2: [self.issue_2.issue_id],
+      3: [self.issue_3.issue_id]
+      }
+
+    prev_iid, index, next_iid = pipeline.DetermineIssuePosition(self.issue_3)
+    # The total ordering is issue_1, issue_3, issue_2 for high, med, low.
+    self.assertEqual(self.issue_1.issue_id, prev_iid)
+    self.assertEqual(1, index)
+    self.assertEqual(self.issue_2.issue_id, next_iid)
+
+  def testDetermineIssuePosition_NotInResults(self):
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+    # In this unit test case we are not calling SearchForIIDs(), instead just
+    # set pipeline.filtered_iids directly.
+    pipeline.filtered_iids = {
+      0: [],
+      1: [self.issue_1.issue_id],
+      2: [self.issue_2.issue_id],
+      3: []
+      }
+
+    prev_iid, index, next_iid = pipeline.DetermineIssuePosition(self.issue_3)
+    # The total ordering is issue_1, issue_3, issue_2 for high, med, low.
+    self.assertEqual(None, prev_iid)
+    self.assertEqual(None, index)
+    self.assertEqual(None, next_iid)
+
+  def testDetermineIssuePositionInShard_IssueIsInShard(self):
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+    # Let's assume issues 1, 2, and 3 are all in the same shard.
+    pipeline.filtered_iids = {
+      0: [self.issue_1.issue_id, self.issue_2.issue_id, self.issue_3.issue_id],
+      }
+
+    # The total ordering is issue_1, issue_3, issue_2 for high, med, low.
+    prev_cand, index, next_cand = pipeline._DetermineIssuePositionInShard(
+      0, self.issue_1, {})
+    self.assertEqual(None, prev_cand)
+    self.assertEqual(0, index)
+    self.assertEqual(self.issue_3, next_cand)
+
+    prev_cand, index, next_cand = pipeline._DetermineIssuePositionInShard(
+      0, self.issue_3, {})
+    self.assertEqual(self.issue_1, prev_cand)
+    self.assertEqual(1, index)
+    self.assertEqual(self.issue_2, next_cand)
+
+    prev_cand, index, next_cand = pipeline._DetermineIssuePositionInShard(
+      0, self.issue_2, {})
+    self.assertEqual(self.issue_3, prev_cand)
+    self.assertEqual(2, index)
+    self.assertEqual(None, next_cand)
+
+  def testDetermineIssuePositionInShard_IssueIsNotInShard(self):
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+
+    # The total ordering is issue_1, issue_3, issue_2 for high, med, low.
+    pipeline.filtered_iids = {
+      0: [self.issue_2.issue_id, self.issue_3.issue_id],
+      }
+    prev_cand, index, next_cand = pipeline._DetermineIssuePositionInShard(
+      0, self.issue_1, {})
+    self.assertEqual(None, prev_cand)
+    self.assertEqual(0, index)
+    self.assertEqual(self.issue_3, next_cand)
+
+    pipeline.filtered_iids = {
+      0: [self.issue_1.issue_id, self.issue_2.issue_id],
+      }
+    prev_cand, index, next_cand = pipeline._DetermineIssuePositionInShard(
+      0, self.issue_3, {})
+    self.assertEqual(self.issue_1, prev_cand)
+    self.assertEqual(1, index)
+    self.assertEqual(self.issue_2, next_cand)
+
+    pipeline.filtered_iids = {
+      0: [self.issue_1.issue_id, self.issue_3.issue_id],
+      }
+    prev_cand, index, next_cand = pipeline._DetermineIssuePositionInShard(
+      0, self.issue_2, {})
+    self.assertEqual(self.issue_3, prev_cand)
+    self.assertEqual(2, index)
+    self.assertEqual(None, next_cand)
+
+  def testFetchAllSamples_Empty(self):
+    filtered_iids = {}
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+    samples_by_shard, sample_iids_to_shard = pipeline._FetchAllSamples(
+        filtered_iids)
+    self.assertEqual({}, samples_by_shard)
+    self.assertEqual({}, sample_iids_to_shard)
+
+  def testFetchAllSamples_SmallResultsPerShard(self):
+    filtered_iids = {
+        0: [100, 110, 120],
+        1: [101, 111, 121],
+        }
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+
+    samples_by_shard, sample_iids_to_shard = pipeline._FetchAllSamples(
+        filtered_iids)
+    self.assertEqual(2, len(samples_by_shard))
+    self.assertEqual(0, len(sample_iids_to_shard))
+
+  def testFetchAllSamples_Normal(self):
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+    issues = self.MakeIssues(23)
+    filtered_iids = {
+        0: [issue.issue_id for issue in issues],
+        }
+
+    samples_by_shard, sample_iids_to_shard = pipeline._FetchAllSamples(
+        filtered_iids)
+    self.assertEqual(1, len(samples_by_shard))
+    self.assertEqual(2, len(samples_by_shard[0]))
+    self.assertEqual(2, len(sample_iids_to_shard))
+    for sample_iid in sample_iids_to_shard:
+      shard_key = sample_iids_to_shard[sample_iid]
+      self.assertIn(sample_iid, filtered_iids[shard_key])
+
+  def testChooseSampleIssues_Empty(self):
+    """When the search gave no results, there cannot be any samples."""
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+    issue_ids = []
+    on_hand_issues, needed_iids = pipeline._ChooseSampleIssues(issue_ids)
+    self.assertEqual({}, on_hand_issues)
+    self.assertEqual([], needed_iids)
+
+  def testChooseSampleIssues_Small(self):
+    """When the search gave few results, don't bother with samples."""
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+    issue_ids = [78901, 78902]
+    on_hand_issues, needed_iids = pipeline._ChooseSampleIssues(issue_ids)
+    self.assertEqual({}, on_hand_issues)
+    self.assertEqual([], needed_iids)
+
+  def MakeIssues(self, num_issues):
+    issues = []
+    for i in range(num_issues):
+      issue = fake.MakeTestIssue(789, 100 + i, 'samp test', 'New', 111)
+      issues.append(issue)
+      self.services.issue.TestAddIssue(issue)
+    return issues
+
+  def testChooseSampleIssues_Normal(self):
+    """We will choose at least one sample for every 10 results in a shard."""
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+    issues = self.MakeIssues(23)
+    issue_ids = [issue.issue_id for issue in issues]
+    on_hand_issues, needed_iids = pipeline._ChooseSampleIssues(issue_ids)
+    self.assertEqual({}, on_hand_issues)
+    self.assertEqual(2, len(needed_iids))
+    for sample_iid in needed_iids:
+      self.assertIn(sample_iid, issue_ids)
+
+  def testLookupNeededUsers(self):
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+
+    pipeline._LookupNeededUsers([])
+    self.assertEqual([], list(pipeline.users_by_id.keys()))
+
+    pipeline._LookupNeededUsers([self.issue_1, self.issue_2, self.issue_3])
+    self.assertEqual([0, 111], list(pipeline.users_by_id.keys()))
+
+  def testPaginate_List(self):
+    pipeline = frontendsearchpipeline.FrontendSearchPipeline(
+        self.cnxn,
+        self.services,
+        self.auth,
+        self.me_user_id,
+        self.query,
+        self.query_project_names,
+        self.items_per_page,
+        self.paginate_start,
+        self.can,
+        self.group_by_spec,
+        self.sort_spec,
+        self.warnings,
+        self.errors,
+        self.use_cached_searches,
+        self.profiler,
+        project=self.project)
+    pipeline.allowed_iids = [
+      self.issue_1.issue_id, self.issue_2.issue_id, self.issue_3.issue_id]
+    pipeline.allowed_results = [self.issue_1, self.issue_2, self.issue_3]
+    pipeline.total_count = len(pipeline.allowed_results)
+    pipeline.Paginate()
+    self.assertEqual(
+      [self.issue_1, self.issue_2, self.issue_3],
+      pipeline.visible_results)
+    self.assertFalse(pipeline.pagination.limit_reached)
+
+
+class FrontendSearchPipelineMethodsTest(unittest.TestCase):
+
+  def setUp(self):
+    self.mox = mox.Mox()
+    self.testbed = testbed.Testbed()
+    self.testbed.activate()
+    self.testbed.init_user_stub()
+    self.testbed.init_memcache_stub()
+
+    self.project_id = 789
+    self.default_config = tracker_bizobj.MakeDefaultProjectIssueConfig(
+        self.project_id)
+    self.services = service_manager.Services(
+        project=fake.ProjectService())
+    self.project = self.services.project.TestAddProject(
+        'proj', project_id=self.project_id)
+
+  def tearDown(self):
+    self.testbed.deactivate()
+    self.mox.UnsetStubs()
+    self.mox.ResetAll()
+
+  def testMakeBackendCallback(self):
+    called_with = []
+
+    def func(a, b):
+      called_with.append((a, b))
+
+    callback = frontendsearchpipeline._MakeBackendCallback(func, 10, 20)
+    callback()
+    self.assertEqual([(10, 20)], called_with)
+
+  def testParseUserQuery_CheckQuery(self):
+    warnings = []
+    msg = frontendsearchpipeline._CheckQuery(
+        'cnxn', self.services, 'ok query', self.default_config,
+        [self.project_id], True, warnings=warnings)
+    self.assertIsNone(msg)
+    self.assertEqual([], warnings)
+
+    warnings = []
+    msg = frontendsearchpipeline._CheckQuery(
+        'cnxn', self.services, 'modified:0-0-0', self.default_config,
+        [self.project_id], True, warnings=warnings)
+    self.assertEqual(
+        'Could not parse date: 0-0-0',
+        msg)
+
+    warnings = []
+    msg = frontendsearchpipeline._CheckQuery(
+        'cnxn', self.services, 'blocking:3.14', self.default_config,
+        [self.project_id], True, warnings=warnings)
+    self.assertEqual(
+        'Could not parse issue reference: 3.14',
+        msg)
+    self.assertEqual([], warnings)
+
+  def testStartBackendSearch(self):
+    # TODO(jrobbins): write this test.
+    pass
+
+  def testFinishBackendSearch(self):
+    # TODO(jrobbins): write this test.
+    pass
+
+  def testGetProjectTimestamps_NoneSet(self):
+    project_shard_timestamps = frontendsearchpipeline._GetProjectTimestamps(
+      [], [])
+    self.assertEqual({}, project_shard_timestamps)
+
+    project_shard_timestamps = frontendsearchpipeline._GetProjectTimestamps(
+      [], [(0, (0, 'p:v')), (1, (1, 'p:v')), (2, (2, 'p:v'))])
+    self.assertEqual({}, project_shard_timestamps)
+
+    project_shard_timestamps = frontendsearchpipeline._GetProjectTimestamps(
+      [789], [(0, (0, 'p:v')), (1, (1, 'p:v')), (2, (2, 'p:v'))])
+    self.assertEqual({}, project_shard_timestamps)
+
+  def testGetProjectTimestamps_SpecificProjects(self):
+    memcache.set('789;0', NOW)
+    memcache.set('789;1', NOW - 1000)
+    memcache.set('789;2', NOW - 3000)
+    project_shard_timestamps = frontendsearchpipeline._GetProjectTimestamps(
+      [789], [(0, (0, 'p:v')), (1, (1, 'p:v')), (2, (2, 'p:v'))])
+    self.assertEqual(
+      { (789, 0): NOW,
+        (789, 1): NOW - 1000,
+        (789, 2): NOW - 3000,
+        },
+      project_shard_timestamps)
+
+    memcache.set('790;0', NOW)
+    memcache.set('790;1', NOW - 10000)
+    memcache.set('790;2', NOW - 30000)
+    project_shard_timestamps = frontendsearchpipeline._GetProjectTimestamps(
+      [789, 790], [(0, (0, 'p:v')), (1, (1, 'p:v')), (2, (2, 'p:v'))])
+    self.assertEqual(
+      { (789, 0): NOW,
+        (789, 1): NOW - 1000,
+        (789, 2): NOW - 3000,
+        (790, 0): NOW,
+        (790, 1): NOW - 10000,
+        (790, 2): NOW - 30000,
+        },
+      project_shard_timestamps)
+
+  def testGetProjectTimestamps_SiteWide(self):
+    memcache.set('all;0', NOW)
+    memcache.set('all;1', NOW - 10000)
+    memcache.set('all;2', NOW - 30000)
+    project_shard_timestamps = frontendsearchpipeline._GetProjectTimestamps(
+      [], [(0, (0, 'p:v')), (1, (1, 'p:v')), (2, (2, 'p:v'))])
+    self.assertEqual(
+      { ('all', 0): NOW,
+        ('all', 1): NOW - 10000,
+        ('all', 2): NOW - 30000,
+        },
+      project_shard_timestamps)
+
+  def testGetNonviewableIIDs_SearchMissSoNoOp(self):
+    """If search cache missed, don't bother looking up nonviewable IIDs."""
+    unfiltered_iids_dict = {}  # No cached search results found.
+    rpc_tuples = []  # Nothing should accumulate here in this case.
+    nonviewable_iids = {}  # Nothing should accumulate here in this case.
+    processed_invalidations_up_to = 12345
+    frontendsearchpipeline._GetNonviewableIIDs(
+        [789], 111, list(unfiltered_iids_dict.keys()), rpc_tuples,
+        nonviewable_iids, {}, processed_invalidations_up_to, True)
+    self.assertEqual([], rpc_tuples)
+    self.assertEqual({}, nonviewable_iids)
+
+  def testGetNonviewableIIDs_SearchHitThenNonviewableHit(self):
+    """If search cache hit, get nonviewable info from cache."""
+    unfiltered_iids_dict = {
+      1: [10001, 10021],
+      2: ['the search result issue_ids do not matter'],
+      }
+    rpc_tuples = []  # Nothing should accumulate here in this case.
+    nonviewable_iids = {}  # Our mock results should end up here.
+    processed_invalidations_up_to = 12345
+    memcache.set('nonviewable:789;111;1',
+                 ([10001, 10031], processed_invalidations_up_to - 10))
+    memcache.set('nonviewable:789;111;2',
+                 ([10002, 10042], processed_invalidations_up_to - 30))
+
+    project_shard_timestamps = {
+      (789, 1): 0,  # not stale
+      (789, 2): 0,  # not stale
+      }
+    frontendsearchpipeline._GetNonviewableIIDs(
+        [789], 111, list(unfiltered_iids_dict.keys()), rpc_tuples,
+        nonviewable_iids, project_shard_timestamps,
+        processed_invalidations_up_to, True)
+    self.assertEqual([], rpc_tuples)
+    self.assertEqual({1: {10001, 10031}, 2: {10002, 10042}}, nonviewable_iids)
+
+  def testGetNonviewableIIDs_SearchHitNonviewableMissSoStartRPC(self):
+    """If search hit and n-v miss, create RPCs to get nonviewable info."""
+    self.mox.StubOutWithMock(
+        frontendsearchpipeline, '_StartBackendNonviewableCall')
+    unfiltered_iids_dict = {
+      2: ['the search result issue_ids do not matter'],
+      }
+    rpc_tuples = []  # One RPC object should accumulate here.
+    nonviewable_iids = {}  # This will stay empty until RPCs complete.
+    processed_invalidations_up_to = 12345
+    # Nothing is set in memcache for this case.
+    a_fake_rpc = testing_helpers.Blank(callback=None)
+    frontendsearchpipeline._StartBackendNonviewableCall(
+      789, 111, 2, processed_invalidations_up_to).AndReturn(a_fake_rpc)
+    self.mox.ReplayAll()
+
+    frontendsearchpipeline._GetNonviewableIIDs(
+        [789], 111, list(unfiltered_iids_dict.keys()), rpc_tuples,
+        nonviewable_iids, {}, processed_invalidations_up_to, True)
+    self.mox.VerifyAll()
+    _, sid_0, rpc_0 = rpc_tuples[0]
+    self.assertEqual(2, sid_0)
+    self.assertEqual({}, nonviewable_iids)
+    self.assertEqual(a_fake_rpc, rpc_0)
+    self.assertIsNotNone(a_fake_rpc.callback)
+
+  def testAccumulateNonviewableIIDs_MemcacheHitForProject(self):
+    processed_invalidations_up_to = 12345
+    cached_dict = {
+      '789;111;2': ([10002, 10042], processed_invalidations_up_to - 10),
+      '789;111;3': ([10003, 10093], processed_invalidations_up_to - 30),
+      }
+    rpc_tuples = []  # Nothing should accumulate here.
+    nonviewable_iids = {1: {10001}}  # This will gain the shard 2 values.
+    project_shard_timestamps = {
+      (789, 1): 0,  # not stale
+      (789, 2): 0,  # not stale
+      }
+    frontendsearchpipeline._AccumulateNonviewableIIDs(
+      789, 111, 2, cached_dict, nonviewable_iids, project_shard_timestamps,
+      rpc_tuples, processed_invalidations_up_to)
+    self.assertEqual([], rpc_tuples)
+    self.assertEqual({1: {10001}, 2: {10002, 10042}}, nonviewable_iids)
+
+  def testAccumulateNonviewableIIDs_MemcacheStaleForProject(self):
+    self.mox.StubOutWithMock(
+      frontendsearchpipeline, '_StartBackendNonviewableCall')
+    processed_invalidations_up_to = 12345
+    cached_dict = {
+      '789;111;2': ([10002, 10042], processed_invalidations_up_to - 10),
+      '789;111;3': ([10003, 10093], processed_invalidations_up_to - 30),
+      }
+    rpc_tuples = []  # Nothing should accumulate here.
+    nonviewable_iids = {1: {10001}}  # Nothing added here until RPC completes
+    project_shard_timestamps = {
+      (789, 1): 0,  # not stale
+      (789, 2): processed_invalidations_up_to,  # stale!
+      }
+    a_fake_rpc = testing_helpers.Blank(callback=None)
+    frontendsearchpipeline._StartBackendNonviewableCall(
+      789, 111, 2, processed_invalidations_up_to).AndReturn(a_fake_rpc)
+    self.mox.ReplayAll()
+
+    frontendsearchpipeline._AccumulateNonviewableIIDs(
+      789, 111, 2, cached_dict, nonviewable_iids, project_shard_timestamps,
+      rpc_tuples, processed_invalidations_up_to)
+    self.mox.VerifyAll()
+    _, sid_0, rpc_0 = rpc_tuples[0]
+    self.assertEqual(2, sid_0)
+    self.assertEqual(a_fake_rpc, rpc_0)
+    self.assertIsNotNone(a_fake_rpc.callback)
+    self.assertEqual({1: {10001}}, nonviewable_iids)
+
+  def testAccumulateNonviewableIIDs_MemcacheHitForWholeSite(self):
+    processed_invalidations_up_to = 12345
+    cached_dict = {
+      'all;111;2': ([10002, 10042], processed_invalidations_up_to - 10),
+      'all;111;3': ([10003, 10093], processed_invalidations_up_to - 30),
+      }
+    rpc_tuples = []  # Nothing should accumulate here.
+    nonviewable_iids = {1: {10001}}  # This will gain the shard 2 values.
+    project_shard_timestamps = {
+      (None, 1): 0,  # not stale
+      (None, 2): 0,  # not stale
+      }
+    frontendsearchpipeline._AccumulateNonviewableIIDs(
+      None, 111, 2, cached_dict, nonviewable_iids, project_shard_timestamps,
+      rpc_tuples, processed_invalidations_up_to)
+    self.assertEqual([], rpc_tuples)
+    self.assertEqual({1: {10001}, 2: {10002, 10042}}, nonviewable_iids)
+
+  def testAccumulateNonviewableIIDs_MemcacheMissSoStartRPC(self):
+    self.mox.StubOutWithMock(
+        frontendsearchpipeline, '_StartBackendNonviewableCall')
+    cached_dict = {}  # Nothing here, so it is an at-risk cache miss.
+    rpc_tuples = []  # One RPC should accumulate here.
+    nonviewable_iids = {1: {10001}}  # Nothing added here until RPC completes.
+    processed_invalidations_up_to = 12345
+    a_fake_rpc = testing_helpers.Blank(callback=None)
+    frontendsearchpipeline._StartBackendNonviewableCall(
+      789, 111, 2, processed_invalidations_up_to).AndReturn(a_fake_rpc)
+    self.mox.ReplayAll()
+
+    frontendsearchpipeline._AccumulateNonviewableIIDs(
+      789, 111, 2, cached_dict, nonviewable_iids, {}, rpc_tuples,
+      processed_invalidations_up_to)
+    self.mox.VerifyAll()
+    _, sid_0, rpc_0 = rpc_tuples[0]
+    self.assertEqual(2, sid_0)
+    self.assertEqual(a_fake_rpc, rpc_0)
+    self.assertIsNotNone(a_fake_rpc.callback)
+    self.assertEqual({1: {10001}}, nonviewable_iids)
+
+  def testGetCachedSearchResults(self):
+    # TODO(jrobbins): Write this test.
+    pass
+
+  def testMakeBackendRequestHeaders(self):
+    headers = frontendsearchpipeline._MakeBackendRequestHeaders(False)
+    self.assertNotIn('X-AppEngine-FailFast', headers)
+    headers = frontendsearchpipeline._MakeBackendRequestHeaders(True)
+    self.assertEqual('Yes', headers['X-AppEngine-FailFast'])
+
+  def testStartBackendSearchCall(self):
+    self.mox.StubOutWithMock(urlfetch, 'create_rpc')
+    self.mox.StubOutWithMock(urlfetch, 'make_fetch_call')
+    self.mox.StubOutWithMock(modules, 'get_hostname')
+    a_fake_rpc = testing_helpers.Blank(callback=None)
+    urlfetch.create_rpc(deadline=settings.backend_deadline).AndReturn(
+      a_fake_rpc)
+    modules.get_hostname(module='besearch')
+    urlfetch.make_fetch_call(
+      a_fake_rpc, mox.StrContains(
+          urls.BACKEND_SEARCH + '?groupby=cc&invalidation_timestep=12345&'
+          +'logged_in_user_id=777&me_user_ids=555&'
+          +'num=201&projects=proj&q=priority%3Dhigh&shard_id=2&start=0'),
+          follow_redirects=False,
+      headers=mox.IsA(dict))
+    self.mox.ReplayAll()
+
+    processed_invalidations_up_to = 12345
+    me_user_ids = [555]
+    logged_in_user_id = 777
+    new_url_num = 201
+    frontendsearchpipeline._StartBackendSearchCall(
+        ['proj'], (2, 'priority=high'),
+        processed_invalidations_up_to,
+        me_user_ids,
+        logged_in_user_id,
+        new_url_num,
+        group_by_spec='cc')
+    self.mox.VerifyAll()
+
+  def testStartBackendSearchCall_SortAndGroup(self):
+    self.mox.StubOutWithMock(urlfetch, 'create_rpc')
+    self.mox.StubOutWithMock(urlfetch, 'make_fetch_call')
+    self.mox.StubOutWithMock(modules, 'get_hostname')
+    a_fake_rpc = testing_helpers.Blank(callback=None)
+    urlfetch.create_rpc(deadline=settings.backend_deadline).AndReturn(
+      a_fake_rpc)
+    modules.get_hostname(module='besearch')
+    urlfetch.make_fetch_call(
+        a_fake_rpc,
+        mox.StrContains(
+            urls.BACKEND_SEARCH + '?groupby=bar&' +
+            'invalidation_timestep=12345&' +
+            'logged_in_user_id=777&me_user_ids=555&num=201&projects=proj&' +
+            'q=priority%3Dhigh&shard_id=2&sort=foo&start=0'),
+        follow_redirects=False,
+        headers=mox.IsA(dict))
+    self.mox.ReplayAll()
+
+    processed_invalidations_up_to = 12345
+    me_user_ids = [555]
+    logged_in_user_id = 777
+    new_url_num = 201
+    sort_spec = 'foo'
+    group_by_spec = 'bar'
+    frontendsearchpipeline._StartBackendSearchCall(
+        ['proj'], (2, 'priority=high'),
+        processed_invalidations_up_to,
+        me_user_ids,
+        logged_in_user_id,
+        new_url_num,
+        sort_spec=sort_spec,
+        group_by_spec=group_by_spec)
+    self.mox.VerifyAll()
+
+  def testStartBackendNonviewableCall(self):
+    self.mox.StubOutWithMock(urlfetch, 'create_rpc')
+    self.mox.StubOutWithMock(urlfetch, 'make_fetch_call')
+    self.mox.StubOutWithMock(modules, 'get_hostname')
+    a_fake_rpc = testing_helpers.Blank(callback=None)
+    urlfetch.create_rpc(deadline=settings.backend_deadline).AndReturn(
+      a_fake_rpc)
+    modules.get_hostname(module='besearch')
+    urlfetch.make_fetch_call(
+      a_fake_rpc, mox.StrContains(urls.BACKEND_NONVIEWABLE),
+      follow_redirects=False, headers=mox.IsA(dict))
+    self.mox.ReplayAll()
+
+    processed_invalidations_up_to = 12345
+    frontendsearchpipeline._StartBackendNonviewableCall(
+      789, 111, 2, processed_invalidations_up_to)
+    self.mox.VerifyAll()
+
+  def testHandleBackendSearchResponse_500(self):
+    response_str = 'There was a problem processing the query.'
+    rpc = testing_helpers.Blank(
+      get_result=lambda: testing_helpers.Blank(
+          content=response_str, status_code=500))
+    rpc_tuple = (NOW, 2, rpc)
+    rpc_tuples = []  # Nothing should be added for this case.
+    filtered_iids = {}  # Search results should accumlate here, per-shard.
+    search_limit_reached = {}  # Booleans accumulate here, per-shard.
+    processed_invalidations_up_to = 12345
+
+    me_user_ids = [111]
+    logged_in_user_id = 0
+    new_url_num = 100
+    error_responses = set()
+
+    self.mox.StubOutWithMock(frontendsearchpipeline, '_StartBackendSearchCall')
+    frontendsearchpipeline._HandleBackendSearchResponse(
+        ['proj'], rpc_tuple, rpc_tuples, 0, filtered_iids, search_limit_reached,
+        processed_invalidations_up_to, error_responses, me_user_ids,
+        logged_in_user_id, new_url_num, 1, None, None)
+    self.assertEqual([], rpc_tuples)
+    self.assertIn(2, error_responses)
+
+  def testHandleBackendSearchResponse_Error(self):
+    response_str = (
+      '})]\'\n'
+      '{'
+      ' "unfiltered_iids": [],'
+      ' "search_limit_reached": false,'
+      ' "error": "Invalid query"'
+      '}'
+      )
+    rpc = testing_helpers.Blank(
+      get_result=lambda: testing_helpers.Blank(
+          content=response_str, status_code=200))
+    rpc_tuple = (NOW, 2, rpc)
+    rpc_tuples = []  # Nothing should be added for this case.
+    filtered_iids = {}  # Search results should accumlate here, per-shard.
+    search_limit_reached = {}  # Booleans accumulate here, per-shard.
+    processed_invalidations_up_to = 12345
+
+    me_user_ids = [111]
+    logged_in_user_id = 0
+    new_url_num = 100
+    error_responses = set()
+    frontendsearchpipeline._HandleBackendSearchResponse(
+        ['proj'], rpc_tuple, rpc_tuples, 2, filtered_iids, search_limit_reached,
+        processed_invalidations_up_to, error_responses, me_user_ids,
+        logged_in_user_id, new_url_num, 1, None, None)
+    self.assertEqual([], rpc_tuples)
+    self.assertEqual({2: []}, filtered_iids)
+    self.assertEqual({2: False}, search_limit_reached)
+    self.assertEqual({2}, error_responses)
+
+  def testHandleBackendSearchResponse_Normal(self):
+    response_str = (
+      '})]\'\n'
+      '{'
+      ' "unfiltered_iids": [10002, 10042],'
+      ' "search_limit_reached": false'
+      '}'
+      )
+    rpc = testing_helpers.Blank(
+      get_result=lambda: testing_helpers.Blank(
+          content=response_str, status_code=200))
+    rpc_tuple = (NOW, 2, rpc)
+    rpc_tuples = []  # Nothing should be added for this case.
+    filtered_iids = {}  # Search results should accumlate here, per-shard.
+    search_limit_reached = {}  # Booleans accumulate here, per-shard.
+    processed_invalidations_up_to = 12345
+
+    me_user_ids = [111]
+    logged_in_user_id = 0
+    new_url_num = 100
+    error_responses = set()
+    frontendsearchpipeline._HandleBackendSearchResponse(
+        ['proj'], rpc_tuple, rpc_tuples, 2, filtered_iids, search_limit_reached,
+        processed_invalidations_up_to, error_responses, me_user_ids,
+        logged_in_user_id, new_url_num, 1, None, None)
+    self.assertEqual([], rpc_tuples)
+    self.assertEqual({2: [10002, 10042]}, filtered_iids)
+    self.assertEqual({2: False}, search_limit_reached)
+
+  def testHandleBackendSearchResponse_TriggersRetry(self):
+    response_str = None
+    rpc = testing_helpers.Blank(
+      get_result=lambda: testing_helpers.Blank(content=response_str))
+    rpc_tuple = (NOW, 2, rpc)
+    rpc_tuples = []  # New RPC should be appended here
+    filtered_iids = {}  # No change here until retry completes.
+    search_limit_reached = {}  # No change here until retry completes.
+    processed_invalidations_up_to = 12345
+    error_responses = set()
+
+    me_user_ids = [111]
+    logged_in_user_id = 0
+    new_url_num = 100
+
+    self.mox.StubOutWithMock(frontendsearchpipeline, '_StartBackendSearchCall')
+    a_fake_rpc = testing_helpers.Blank(callback=None)
+    rpc = frontendsearchpipeline._StartBackendSearchCall(
+        ['proj'],
+        2,
+        processed_invalidations_up_to,
+        me_user_ids,
+        logged_in_user_id,
+        new_url_num,
+        can=1,
+        group_by_spec=None,
+        sort_spec=None,
+        failfast=False).AndReturn(a_fake_rpc)
+    self.mox.ReplayAll()
+
+    frontendsearchpipeline._HandleBackendSearchResponse(
+        ['proj'], rpc_tuple, rpc_tuples, 2, filtered_iids, search_limit_reached,
+        processed_invalidations_up_to, error_responses, me_user_ids,
+        logged_in_user_id, new_url_num, 1, None, None)
+    self.mox.VerifyAll()
+    _, retry_shard_id, retry_rpc = rpc_tuples[0]
+    self.assertEqual(2, retry_shard_id)
+    self.assertEqual(a_fake_rpc, retry_rpc)
+    self.assertIsNotNone(retry_rpc.callback)
+    self.assertEqual({}, filtered_iids)
+    self.assertEqual({}, search_limit_reached)
+
+  def testHandleBackendNonviewableResponse_Error(self):
+    response_str = 'There was an error.'
+    rpc = testing_helpers.Blank(
+      get_result=lambda: testing_helpers.Blank(
+          content=response_str,
+          status_code=500
+      ))
+    rpc_tuple = (NOW, 2, rpc)
+    rpc_tuples = []  # Nothing should be added for this case.
+    nonviewable_iids = {}  # At-risk issue IDs should accumlate here, per-shard.
+    processed_invalidations_up_to = 12345
+
+    self.mox.StubOutWithMock(
+        frontendsearchpipeline, '_StartBackendNonviewableCall')
+    frontendsearchpipeline._HandleBackendNonviewableResponse(
+      789, 111, 2, rpc_tuple, rpc_tuples, 0, nonviewable_iids,
+      processed_invalidations_up_to)
+    self.assertEqual([], rpc_tuples)
+    self.assertNotEqual({2: {10002, 10042}}, nonviewable_iids)
+
+  def testHandleBackendNonviewableResponse_Normal(self):
+    response_str = (
+      '})]\'\n'
+      '{'
+      ' "nonviewable": [10002, 10042]'
+      '}'
+      )
+    rpc = testing_helpers.Blank(
+      get_result=lambda: testing_helpers.Blank(
+          content=response_str,
+          status_code=200
+      ))
+    rpc_tuple = (NOW, 2, rpc)
+    rpc_tuples = []  # Nothing should be added for this case.
+    nonviewable_iids = {}  # At-risk issue IDs should accumlate here, per-shard.
+    processed_invalidations_up_to = 12345
+
+    frontendsearchpipeline._HandleBackendNonviewableResponse(
+      789, 111, 2, rpc_tuple, rpc_tuples, 2, nonviewable_iids,
+      processed_invalidations_up_to)
+    self.assertEqual([], rpc_tuples)
+    self.assertEqual({2: {10002, 10042}}, nonviewable_iids)
+
+  def testHandleBackendAtRiskResponse_TriggersRetry(self):
+    response_str = None
+    rpc = testing_helpers.Blank(
+      get_result=lambda: testing_helpers.Blank(content=response_str))
+    rpc_tuple = (NOW, 2, rpc)
+    rpc_tuples = []  # New RPC should be appended here
+    nonviewable_iids = {}  # No change here until retry completes.
+    processed_invalidations_up_to = 12345
+
+    self.mox.StubOutWithMock(
+      frontendsearchpipeline, '_StartBackendNonviewableCall')
+    a_fake_rpc = testing_helpers.Blank(callback=None)
+    rpc = frontendsearchpipeline._StartBackendNonviewableCall(
+      789, 111, 2, processed_invalidations_up_to, failfast=False
+      ).AndReturn(a_fake_rpc)
+    self.mox.ReplayAll()
+
+    frontendsearchpipeline._HandleBackendNonviewableResponse(
+      789, 111, 2, rpc_tuple, rpc_tuples, 2, nonviewable_iids,
+      processed_invalidations_up_to)
+    self.mox.VerifyAll()
+    _, retry_shard_id, retry_rpc = rpc_tuples[0]
+    self.assertEqual(2, retry_shard_id)
+    self.assertIsNotNone(retry_rpc.callback)
+    self.assertEqual(a_fake_rpc, retry_rpc)
+    self.assertEqual({}, nonviewable_iids)
+
+  def testSortIssues(self):
+    services = service_manager.Services(
+        cache_manager=fake.CacheManager())
+    sorting.InitializeArtValues(services)
+
+    issue_1 = fake.MakeTestIssue(
+      789, 1, 'one', 'New', 111, labels=['Priority-High'])
+    issue_2 = fake.MakeTestIssue(
+      789, 2, 'two', 'New', 111, labels=['Priority-Low'])
+    issue_3 = fake.MakeTestIssue(
+      789, 3, 'three', 'New', 111, labels=['Priority-Medium'])
+    issues = [issue_1, issue_2, issue_3]
+    config = tracker_bizobj.MakeDefaultProjectIssueConfig(789)
+
+    sorted_issues = frontendsearchpipeline._SortIssues(
+        issues, config, {}, '', 'priority')
+
+    self.assertEqual(
+      [issue_1, issue_3, issue_2],  # Order is high, medium, low.
+      sorted_issues)
+
+
+class FrontendSearchPipelineShardMethodsTest(unittest.TestCase):
+
+  def setUp(self):
+    self.sharded_iids = {
+      (0, 'p:v'): [10, 20, 30, 40, 50],
+      (1, 'p:v'): [21, 41, 61, 81],
+      (2, 'p:v'): [42, 52, 62, 72, 102],
+      (3, 'p:v'): [],
+      }
+
+  def testTotalLength_Empty(self):
+    """If there were no results, the length of the sharded list is zero."""
+    self.assertEqual(0, frontendsearchpipeline._TotalLength({}))
+
+  def testTotalLength_Normal(self):
+    """The length of the sharded list is the sum of the shard lengths."""
+    self.assertEqual(
+        14, frontendsearchpipeline._TotalLength(self.sharded_iids))
+
+  def testReverseShards_Empty(self):
+    """Reversing an empty sharded list is still empty."""
+    empty_sharded_iids = {}
+    frontendsearchpipeline._ReverseShards(empty_sharded_iids)
+    self.assertEqual({}, empty_sharded_iids)
+
+  def testReverseShards_Normal(self):
+    """Reversing a sharded list reverses each shard."""
+    frontendsearchpipeline._ReverseShards(self.sharded_iids)
+    self.assertEqual(
+        {(0, 'p:v'): [50, 40, 30, 20, 10],
+         (1, 'p:v'): [81, 61, 41, 21],
+         (2, 'p:v'): [102, 72, 62, 52, 42],
+         (3, 'p:v'): [],
+         },
+        self.sharded_iids)
+
+  def testTrimShardedIIDs_Empty(self):
+    """If the sharded list is empty, trimming it makes no change."""
+    empty_sharded_iids = {}
+    frontendsearchpipeline._TrimEndShardedIIDs(empty_sharded_iids, [], 12)
+    self.assertEqual({}, empty_sharded_iids)
+
+    frontendsearchpipeline._TrimEndShardedIIDs(
+        empty_sharded_iids,
+        [(100, (0, 'p:v')), (88, (8, 'p:v')), (99, (9, 'p:v'))],
+        12)
+    self.assertEqual({}, empty_sharded_iids)
+
+  def testTrimShardedIIDs_NoSamples(self):
+    """If there are no samples, we don't trim off any IIDs."""
+    orig_sharded_iids = {
+      shard_id: iids[:] for shard_id, iids in self.sharded_iids.items()}
+    num_trimmed = frontendsearchpipeline._TrimEndShardedIIDs(
+        self.sharded_iids, [], 12)
+    self.assertEqual(0, num_trimmed)
+    self.assertEqual(orig_sharded_iids, self.sharded_iids)
+
+    num_trimmed = frontendsearchpipeline._TrimEndShardedIIDs(
+        self.sharded_iids, [], 1)
+    self.assertEqual(0, num_trimmed)
+    self.assertEqual(orig_sharded_iids, self.sharded_iids)
+
+  def testTrimShardedIIDs_Normal(self):
+    """The first 3 samples contribute all needed IIDs, so trim off the rest."""
+    samples = [(30, (0, 'p:v')), (41, (1, 'p:v')), (62, (2, 'p:v')),
+               (40, (0, 'p:v')), (81, (1, 'p:v'))]
+    num_trimmed = frontendsearchpipeline._TrimEndShardedIIDs(
+        self.sharded_iids, samples, 5)
+    self.assertEqual(2 + 1 + 0 + 0, num_trimmed)
+    self.assertEqual(
+        {  # shard_id: iids before lower-bound + iids before 1st excess sample.
+         (0, 'p:v'): [10, 20] + [30],
+         (1, 'p:v'): [21] + [41, 61],
+         (2, 'p:v'): [42, 52] + [62, 72, 102],
+         (3, 'p:v'): [] + []},
+        self.sharded_iids)
+
+  def testCalcSamplePositions_Empty(self):
+    sharded_iids = {0: []}
+    samples = []
+    self.assertEqual(
+      [], frontendsearchpipeline._CalcSamplePositions(sharded_iids, samples))
+
+    sharded_iids = {0: [10, 20, 30, 40]}
+    samples = []
+    self.assertEqual(
+      [], frontendsearchpipeline._CalcSamplePositions(sharded_iids, samples))
+
+    sharded_iids = {0: []}
+    # E.g., the IIDs 2 and 4 might have been trimmed out in the forward phase.
+    # But we still have them in the list for the backwards phase, and they
+    # should just not contribute anything to the result.
+    samples = [(2, (2, 'p:v')), (4, (4, 'p:v'))]
+    self.assertEqual(
+      [], frontendsearchpipeline._CalcSamplePositions(sharded_iids, samples))
+
+  def testCalcSamplePositions_Normal(self):
+    samples = [(30, (0, 'p:v')), (41, (1, 'p:v')), (62, (2, 'p:v')),
+               (40, (0, 'p:v')), (81, (1, 'p:v'))]
+    self.assertEqual(
+      [(30, (0, 'p:v'), 2),
+       (41, (1, 'p:v'), 1),
+       (62, (2, 'p:v'), 2),
+       (40, (0, 'p:v'), 3),
+       (81, (1, 'p:v'), 3)],
+      frontendsearchpipeline._CalcSamplePositions(self.sharded_iids, samples))