SERVER-27052 moved SyncSourceSelectorMock to its own library

5 files changed, 249 insertions, 100 deletions

diff --git a/src/mongo/db/repl/SConscript b/src/mongo/db/repl/SConscript
index 383514fa7db..0ce2f74901d 100644
--- a/src/mongo/db/repl/SConscript
+++ b/src/mongo/db/repl/SConscript
@@ -770,11 +770,25 @@ env.Library(
     ],
 )
 
+env.Library(
+    target='sync_source_selector_mock',
+    source=[
+        'sync_source_selector_mock.cpp',
+    ],
+    LIBDEPS=[
+        'optime',
+        '$BUILD_DIR/mongo/base',
+        '$BUILD_DIR/mongo/rpc/metadata',
+        '$BUILD_DIR/mongo/util/net/hostandport',
+    ],
+)
+
 env.CppUnitTest(
     target='sync_source_resolver_test',
     source='sync_source_resolver_test.cpp',
     LIBDEPS=[
         'sync_source_resolver',
+        'sync_source_selector_mock',
         '$BUILD_DIR/mongo/executor/thread_pool_task_executor_test_fixture',
         '$BUILD_DIR/mongo/unittest/task_executor_proxy',
     ],
@@ -1051,6 +1065,7 @@ env.CppUnitTest(
         'data_replicator',
         'data_replicator_external_state_mock',
         'replication_executor_test_fixture',
+        'sync_source_selector_mock',
         '$BUILD_DIR/mongo/db/query/command_request_response',
         '$BUILD_DIR/mongo/executor/thread_pool_task_executor_test_fixture',
         '$BUILD_DIR/mongo/unittest/concurrency',
diff --git a/src/mongo/db/repl/data_replicator_test.cpp b/src/mongo/db/repl/data_replicator_test.cpp
index 3a451783597..08ff6cd744a 100644
--- a/src/mongo/db/repl/data_replicator_test.cpp
+++ b/src/mongo/db/repl/data_replicator_test.cpp
@@ -45,6 +45,7 @@
 #include "mongo/db/repl/storage_interface_mock.h"
 #include "mongo/db/repl/sync_source_resolver.h"
 #include "mongo/db/repl/sync_source_selector.h"
+#include "mongo/db/repl/sync_source_selector_mock.h"
 #include "mongo/db/repl/update_position_args.h"
 #include "mongo/executor/network_interface_mock.h"
 #include "mongo/executor/thread_pool_task_executor_test_fixture.h"
@@ -79,28 +80,6 @@ struct CollectionCloneInfo {
     Status status{ErrorCodes::NotYetInitialized, ""};
 };
 
-class SyncSourceSelectorMock : public SyncSourceSelector {
-    MONGO_DISALLOW_COPYING(SyncSourceSelectorMock);
-
-public:
-    SyncSourceSelectorMock(const HostAndPort& syncSource) : _syncSource(syncSource) {}
-    void clearSyncSourceBlacklist() override {}
-    HostAndPort chooseNewSyncSource(const OpTime& ot) override {
-        HostAndPort result = _syncSource;
-        return result;
-    }
-    void blacklistSyncSource(const HostAndPort& host, Date_t until) override {
-        _blacklistedSource = host;
-    }
-    bool shouldChangeSyncSource(const HostAndPort& currentSource,
-                                const rpc::ReplSetMetadata& metadata) override {
-        return false;
-    }
-
-    HostAndPort _syncSource;
-    HostAndPort _blacklistedSource;
-};
-
 class DataReplicatorTest : public executor::ThreadPoolExecutorTest, public SyncSourceSelector {
 public:
     DataReplicatorTest() {}
@@ -113,7 +92,7 @@ public:
     void reset() {
         _setMyLastOptime = [this](const OpTime& opTime) { _myLastOpTime = opTime; };
         _myLastOpTime = OpTime();
-        _syncSourceSelector.reset(new SyncSourceSelectorMock(HostAndPort("localhost", -1)));
+        _syncSourceSelector = stdx::make_unique<SyncSourceSelectorMock>();
     }
 
     // SyncSourceSelector
diff --git a/src/mongo/db/repl/sync_source_resolver_test.cpp b/src/mongo/db/repl/sync_source_resolver_test.cpp
index 1022ef54e26..82ae8ab528c 100644
--- a/src/mongo/db/repl/sync_source_resolver_test.cpp
+++ b/src/mongo/db/repl/sync_source_resolver_test.cpp
@@ -34,6 +34,7 @@
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/repl/sync_source_resolver.h"
 #include "mongo/db/repl/sync_source_selector.h"
+#include "mongo/db/repl/sync_source_selector_mock.h"
 #include "mongo/executor/network_interface_mock.h"
 #include "mongo/executor/thread_pool_task_executor_test_fixture.h"
 #include "mongo/stdx/functional.h"
@@ -67,30 +68,6 @@ private:
     ShouldFailRequestFn _shouldFailRequest;
 };
 
-class SyncSourceSelectorMock : public SyncSourceSelector {
-public:
-    void clearSyncSourceBlacklist() override {}
-    HostAndPort chooseNewSyncSource(const OpTime& ot) override {
-        chooseNewSyncSourceHook();
-        lastOpTimeFetched = ot;
-        return syncSource;
-    }
-    void blacklistSyncSource(const HostAndPort& host, Date_t until) override {
-        blacklistHost = host;
-        blacklistUntil = until;
-    }
-    bool shouldChangeSyncSource(const HostAndPort&, const rpc::ReplSetMetadata&) {
-        return false;
-    }
-
-    HostAndPort syncSource = HostAndPort("host1", 1234);
-    OpTime lastOpTimeFetched;
-    stdx::function<void()> chooseNewSyncSourceHook = []() {};
-
-    HostAndPort blacklistHost;
-    Date_t blacklistUntil;
-};
-
 class SyncSourceResolverTest : public executor::ThreadPoolExecutorTest {
 private:
     void setUp() override;
@@ -241,7 +218,7 @@ TEST_F(SyncSourceResolverTest, StartupReturnsIllegalOperationIfAlreadyActive) {
 }
 
 TEST_F(SyncSourceResolverTest, StartupReturnsShutdownInProgressIfResolverIsShuttingDown) {
-    _selector->syncSource = HostAndPort("node1", 12345);
+    _selector->setChooseNewSyncSourceResult_forTest(HostAndPort("node1", 12345));
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(executor::NetworkInterfaceMock::InNetworkGuard(getNet())->hasReadyRequests());
     _resolver->shutdown();
@@ -258,13 +235,13 @@ TEST_F(SyncSourceResolverTest, StartupReturnsShutdownInProgressIfExecutorIsShutd
 
 TEST_F(SyncSourceResolverTest,
        SyncSourceResolverReturnsStatusOkAndAnEmptyHostWhenNoViableHostExists) {
-    _selector->syncSource = HostAndPort();
+    _selector->setChooseNewSyncSourceResult_forTest(HostAndPort());
     ASSERT_OK(_resolver->startup());
 
     // Resolver invokes callback with empty host and becomes inactive immediately.
     ASSERT_FALSE(_resolver->isActive());
     ASSERT_EQUALS(HostAndPort(), unittest::assertGet(_response.syncSourceStatus));
-    ASSERT_EQUALS(lastOpTimeFetched, _selector->lastOpTimeFetched);
+    ASSERT_EQUALS(lastOpTimeFetched, _selector->getChooseNewSyncSourceOpTime_forTest());
 
     // Cannot restart a completed resolver.
     ASSERT_EQUALS(ErrorCodes::ShutdownInProgress, _resolver->startup());
@@ -273,17 +250,16 @@ TEST_F(SyncSourceResolverTest,
 TEST_F(
     SyncSourceResolverTest,
     SyncSourceResolverReturnsCallbackCanceledIfResolverIsShutdownBeforeReturningEmptySyncSource) {
-    _selector->syncSource = HostAndPort();
-    _selector->chooseNewSyncSourceHook = [this]() { _resolver->shutdown(); };
+    _selector->setChooseNewSyncSourceResult_forTest(HostAndPort());
+    _selector->setChooseNewSyncSourceHook_forTest([this]() { _resolver->shutdown(); });
     ASSERT_EQUALS(ErrorCodes::CallbackCanceled, _resolver->startup());
     ASSERT_EQUALS(ErrorCodes::CallbackCanceled, _response.syncSourceStatus);
 }
 
 TEST_F(SyncSourceResolverTest,
        SyncSourceResolverConvertsExceptionToStatusIfChoosingViableSyncSourceThrowsException) {
-    _selector->chooseNewSyncSourceHook = [this]() {
-        uassert(ErrorCodes::InternalError, "", false);
-    };
+    _selector->setChooseNewSyncSourceHook_forTest(
+        [this]() { uassert(ErrorCodes::InternalError, "", false); });
     ASSERT_EQUALS(ErrorCodes::InternalError, _resolver->startup());
     ASSERT_EQUALS(ErrorCodes::InternalError, _response.syncSourceStatus);
 }
@@ -313,7 +289,7 @@ void _scheduleFirstOplogEntryFetcherResponse(executor::NetworkInterfaceMock* net
     ASSERT_BSONOBJ_EQ(BSON("$natural" << 1), request.cmdObj.getObjectField("sort"));
 
     // Change next sync source candidate before delivering scheduled response.
-    selector->syncSource = nextSyncSource;
+    selector->setChooseNewSyncSourceResult_forTest(nextSyncSource);
 
     net->runReadyNetworkOperations();
 }
@@ -330,7 +306,7 @@ void _scheduleFirstOplogEntryFetcherResponse(executor::NetworkInterfaceMock* net
 TEST_F(SyncSourceResolverTest,
        SyncSourceResolverReturnsStatusOkAndTheFoundHostWhenAnEligibleSyncSourceExists) {
     HostAndPort candidate1("node1", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
 
@@ -345,7 +321,7 @@ TEST_F(SyncSourceResolverTest,
 TEST_F(SyncSourceResolverTest,
        SyncSourceResolverTransitionsToCompleteWhenFinishCallbackThrowsException) {
     HostAndPort candidate1("node1", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     _onCompletion = [this](const SyncSourceResolverResponse& response) {
         _response = response;
         uassert(ErrorCodes::InternalError, "", false);
@@ -391,7 +367,7 @@ TEST_F(SyncSourceResolverTest,
        SyncSourceResolverWillTryOtherSourcesWhenTheFirstNodeDoesNotHaveOldEnoughData) {
     HostAndPort candidate1("node1", 12345);
     HostAndPort candidate2("node2", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
 
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
@@ -400,9 +376,9 @@ TEST_F(SyncSourceResolverTest,
         getNet(), _selector.get(), candidate1, candidate2, Timestamp(200, 2));
 
     ASSERT_TRUE(_resolver->isActive());
-    ASSERT_EQUALS(candidate1, _selector->blacklistHost);
+    ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
     ASSERT_EQUALS(getExecutor().now() + SyncSourceResolver::kTooStaleBlacklistDuration,
-                  _selector->blacklistUntil);
+                  _selector->getLastBlacklistExpiration_forTest());
 
     _scheduleFirstOplogEntryFetcherResponse(
         getNet(), _selector.get(), candidate2, HostAndPort(), Timestamp(10, 2));
@@ -417,7 +393,7 @@ TEST_F(SyncSourceResolverTest,
     HostAndPort candidate1("node1", 12345);
     HostAndPort candidate2("node2", 12345);
     HostAndPort candidate3("node3", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
 
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
@@ -448,7 +424,7 @@ void _scheduleNetworkErrorForFirstNode(executor::NetworkInterfaceMock* net,
     ASSERT_EQUALS(currentSyncSource, request.target);
 
     // Change next sync source candidate before delivering error to callback.
-    selector->syncSource = nextSyncSource;
+    selector->setChooseNewSyncSourceResult_forTest(nextSyncSource);
 
     net->runReadyNetworkOperations();
 }
@@ -457,7 +433,7 @@ TEST_F(SyncSourceResolverTest,
        SyncSourceResolverWillTryOtherSourcesWhenTheFirstNodeHasANetworkError) {
     HostAndPort candidate1("node1", 12345);
     HostAndPort candidate2("node2", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
 
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
@@ -465,9 +441,9 @@ TEST_F(SyncSourceResolverTest,
     _scheduleNetworkErrorForFirstNode(getNet(), _selector.get(), candidate1, candidate2);
 
     ASSERT_TRUE(_resolver->isActive());
-    ASSERT_EQUALS(candidate1, _selector->blacklistHost);
+    ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
     ASSERT_EQUALS(getExecutor().now() + SyncSourceResolver::kFetcherErrorBlacklistDuration,
-                  _selector->blacklistUntil);
+                  _selector->getLastBlacklistExpiration_forTest());
 
     _scheduleFirstOplogEntryFetcherResponse(
         getNet(), _selector.get(), candidate2, HostAndPort(), Timestamp(10, 2));
@@ -480,7 +456,7 @@ TEST_F(SyncSourceResolverTest,
 TEST_F(SyncSourceResolverTest,
        SyncSourceResolverReturnsEmptyHostWhenNoViableNodeExistsAfterNetworkErrorOnFirstNode) {
     HostAndPort candidate1("node1", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
 
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
@@ -488,9 +464,9 @@ TEST_F(SyncSourceResolverTest,
     _scheduleNetworkErrorForFirstNode(getNet(), _selector.get(), candidate1, HostAndPort());
 
     ASSERT_FALSE(_resolver->isActive());
-    ASSERT_EQUALS(candidate1, _selector->blacklistHost);
+    ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
     ASSERT_EQUALS(getExecutor().now() + SyncSourceResolver::kFetcherErrorBlacklistDuration,
-                  _selector->blacklistUntil);
+                  _selector->getLastBlacklistExpiration_forTest());
 
     ASSERT_EQUALS(HostAndPort(), unittest::assertGet(_response.syncSourceStatus));
 }
@@ -499,7 +475,7 @@ TEST_F(SyncSourceResolverTest,
        SyncSourceResolverReturnsScheduleErrorWhenTheSchedulingCommandToSecondNodeFails) {
     HostAndPort candidate1("node1", 12345);
     HostAndPort candidate2("node2", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
 
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
@@ -511,9 +487,9 @@ TEST_F(SyncSourceResolverTest,
     _scheduleNetworkErrorForFirstNode(getNet(), _selector.get(), candidate1, candidate2);
 
     ASSERT_FALSE(_resolver->isActive());
-    ASSERT_EQUALS(candidate1, _selector->blacklistHost);
+    ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
     ASSERT_EQUALS(getExecutor().now() + SyncSourceResolver::kFetcherErrorBlacklistDuration,
-                  _selector->blacklistUntil);
+                  _selector->getLastBlacklistExpiration_forTest());
 
     ASSERT_EQUALS(ErrorCodes::OperationFailed, _response.syncSourceStatus);
 }
@@ -522,7 +498,7 @@ TEST_F(SyncSourceResolverTest,
        SyncSourceResolverWillTryOtherSourcesWhenTheFirstNodeHasAnEmptyOplog) {
     HostAndPort candidate1("node1", 12345);
     HostAndPort candidate2("node1", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
 
@@ -530,9 +506,9 @@ TEST_F(SyncSourceResolverTest,
         getNet(), _selector.get(), candidate1, candidate2, std::vector<BSONObj>());
 
     ASSERT_TRUE(_resolver->isActive());
-    ASSERT_EQUALS(candidate1, _selector->blacklistHost);
+    ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
     ASSERT_EQUALS(getExecutor().now() + SyncSourceResolver::kOplogEmptyBlacklistDuration,
-                  _selector->blacklistUntil);
+                  _selector->getLastBlacklistExpiration_forTest());
 
     _scheduleFirstOplogEntryFetcherResponse(
         getNet(), _selector.get(), candidate2, HostAndPort(), Timestamp(10, 2));
@@ -546,7 +522,7 @@ TEST_F(SyncSourceResolverTest,
        SyncSourceResolverWillTryOtherSourcesWhenTheFirstNodeHasAnEmptyFirstOplogEntry) {
     HostAndPort candidate1("node1", 12345);
     HostAndPort candidate2("node1", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
 
@@ -554,9 +530,9 @@ TEST_F(SyncSourceResolverTest,
         getNet(), _selector.get(), candidate1, candidate2, {BSONObj()});
 
     ASSERT_TRUE(_resolver->isActive());
-    ASSERT_EQUALS(candidate1, _selector->blacklistHost);
+    ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
     ASSERT_EQUALS(getExecutor().now() + SyncSourceResolver::kFirstOplogEntryEmptyBlacklistDuration,
-                  _selector->blacklistUntil);
+                  _selector->getLastBlacklistExpiration_forTest());
 
     _scheduleFirstOplogEntryFetcherResponse(
         getNet(), _selector.get(), candidate2, HostAndPort(), Timestamp(10, 2));
@@ -570,7 +546,7 @@ TEST_F(SyncSourceResolverTest,
        SyncSourceResolverWillTryOtherSourcesWhenFirstNodeContainsOplogEntryWithNullTimestamp) {
     HostAndPort candidate1("node1", 12345);
     HostAndPort candidate2("node1", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
 
@@ -578,10 +554,10 @@ TEST_F(SyncSourceResolverTest,
         getNet(), _selector.get(), candidate1, candidate2, Timestamp(0, 0));
 
     ASSERT_TRUE(_resolver->isActive());
-    ASSERT_EQUALS(candidate1, _selector->blacklistHost);
+    ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
     ASSERT_EQUALS(getExecutor().now() +
                       SyncSourceResolver::kFirstOplogEntryNullTimestampBlacklistDuration,
-                  _selector->blacklistUntil);
+                  _selector->getLastBlacklistExpiration_forTest());
 
     _scheduleFirstOplogEntryFetcherResponse(
         getNet(), _selector.get(), candidate2, HostAndPort(), Timestamp(10, 2));
@@ -646,7 +622,7 @@ TEST_F(
     _resolver = _makeResolver(lastOpTimeFetched, requiredOpTime);
 
     HostAndPort candidate1("node1", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
 
@@ -668,7 +644,7 @@ TEST_F(SyncSourceResolverTest,
 
     HostAndPort candidate1("node1", 12345);
     HostAndPort candidate2("node2", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
 
@@ -685,9 +661,9 @@ TEST_F(SyncSourceResolverTest,
         {BSON("ts" << requiredOpTime.getTimestamp() << "t" << OpTime::kUninitializedTerm)});
 
     ASSERT_TRUE(_resolver->isActive());
-    ASSERT_EQUALS(candidate1, _selector->blacklistHost);
+    ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
     ASSERT_EQUALS(getExecutor().now() + SyncSourceResolver::kNoRequiredOpTimeBlacklistDuration,
-                  _selector->blacklistUntil);
+                  _selector->getLastBlacklistExpiration_forTest());
 
     _scheduleFirstOplogEntryFetcherResponse(
         getNet(), _selector.get(), candidate2, HostAndPort(), Timestamp(10, 0));
@@ -707,7 +683,7 @@ TEST_F(
 
     HostAndPort candidate1("node1", 12345);
     HostAndPort candidate2("node2", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
 
@@ -719,9 +695,9 @@ TEST_F(
     _scheduleRequiredOpTimeFetcherResponse(getNet(), _selector.get(), candidate1, requiredOpTime);
 
     ASSERT_TRUE(_resolver->isActive());
-    ASSERT_EQUALS(candidate1, _selector->blacklistHost);
+    ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
     ASSERT_EQUALS(getExecutor().now() + SyncSourceResolver::kNoRequiredOpTimeBlacklistDuration,
-                  _selector->blacklistUntil);
+                  _selector->getLastBlacklistExpiration_forTest());
 
     _scheduleFirstOplogEntryFetcherResponse(
         getNet(), _selector.get(), candidate2, HostAndPort(), Timestamp(10, 0));
@@ -739,7 +715,7 @@ TEST_F(SyncSourceResolverTest,
 
     HostAndPort candidate1("node1", 12345);
     HostAndPort candidate2("node2", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
 
@@ -752,9 +728,9 @@ TEST_F(SyncSourceResolverTest,
         getNet(), _selector.get(), candidate1, requiredOpTime, {});
 
     ASSERT_TRUE(_resolver->isActive());
-    ASSERT_EQUALS(candidate1, _selector->blacklistHost);
+    ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
     ASSERT_EQUALS(getExecutor().now() + SyncSourceResolver::kNoRequiredOpTimeBlacklistDuration,
-                  _selector->blacklistUntil);
+                  _selector->getLastBlacklistExpiration_forTest());
 
     _scheduleFirstOplogEntryFetcherResponse(
         getNet(), _selector.get(), candidate2, HostAndPort(), Timestamp(10, 0));
@@ -771,7 +747,7 @@ TEST_F(SyncSourceResolverTest,
 
     HostAndPort candidate1("node1", 12345);
     HostAndPort candidate2("node2", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
 
@@ -788,9 +764,9 @@ TEST_F(SyncSourceResolverTest,
         {BSON("ts" << requiredOpTime.getTimestamp() << "t" << requiredOpTime.getTerm() + 1)});
 
     ASSERT_TRUE(_resolver->isActive());
-    ASSERT_EQUALS(candidate1, _selector->blacklistHost);
+    ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
     ASSERT_EQUALS(getExecutor().now() + SyncSourceResolver::kNoRequiredOpTimeBlacklistDuration,
-                  _selector->blacklistUntil);
+                  _selector->getLastBlacklistExpiration_forTest());
 
     _scheduleFirstOplogEntryFetcherResponse(
         getNet(), _selector.get(), candidate2, HostAndPort(), Timestamp(10, 0));
@@ -810,7 +786,7 @@ TEST_F(SyncSourceResolverTest,
     };
 
     HostAndPort candidate1("node1", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
 
@@ -828,7 +804,7 @@ TEST_F(
     _resolver = _makeResolver(lastOpTimeFetched, requiredOpTime);
 
     HostAndPort candidate1("node1", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
 
@@ -851,7 +827,7 @@ TEST_F(
     _resolver = _makeResolver(lastOpTimeFetched, requiredOpTime);
 
     HostAndPort candidate1("node1", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
 
@@ -873,7 +849,7 @@ TEST_F(
     _resolver = _makeResolver(lastOpTimeFetched, requiredOpTime);
 
     HostAndPort candidate1("node1", 12345);
-    _selector->syncSource = candidate1;
+    _selector->setChooseNewSyncSourceResult_forTest(candidate1);
     ASSERT_OK(_resolver->startup());
     ASSERT_TRUE(_resolver->isActive());
 
@@ -883,9 +859,9 @@ TEST_F(
     _scheduleNetworkErrorForFirstNode(getNet(), _selector.get(), candidate1, HostAndPort());
 
     ASSERT_FALSE(_resolver->isActive());
-    ASSERT_EQUALS(candidate1, _selector->blacklistHost);
+    ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
     ASSERT_EQUALS(getExecutor().now() + SyncSourceResolver::kFetcherErrorBlacklistDuration,
-                  _selector->blacklistUntil);
+                  _selector->getLastBlacklistExpiration_forTest());
 
     _resolver->join();
     ASSERT_FALSE(_resolver->isActive());
diff --git a/src/mongo/db/repl/sync_source_selector_mock.cpp b/src/mongo/db/repl/sync_source_selector_mock.cpp
new file mode 100644
index 00000000000..0b697a2e234
--- /dev/null
+++ b/src/mongo/db/repl/sync_source_selector_mock.cpp
@@ -0,0 +1,80 @@
+/**
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/repl/sync_source_selector_mock.h"
+
+namespace mongo {
+namespace repl {
+
+SyncSourceSelectorMock::SyncSourceSelectorMock() {}
+
+SyncSourceSelectorMock::~SyncSourceSelectorMock() {}
+
+void SyncSourceSelectorMock::clearSyncSourceBlacklist() {}
+
+HostAndPort SyncSourceSelectorMock::chooseNewSyncSource(const OpTime& ot) {
+    _chooseNewSyncSourceHook();
+    _chooseNewSyncSourceOpTime = ot;
+    return _chooseNewSyncSourceResult;
+}
+
+void SyncSourceSelectorMock::blacklistSyncSource(const HostAndPort& host, Date_t until) {
+    _lastBlacklistedSyncSource = host;
+    _lastBlacklistExpiration = until;
+}
+
+void SyncSourceSelectorMock::setChooseNewSyncSourceHook_forTest(
+    const ChooseNewSyncSourceHook& hook) {
+    _chooseNewSyncSourceHook = hook;
+}
+
+bool SyncSourceSelectorMock::shouldChangeSyncSource(const HostAndPort&,
+                                                    const rpc::ReplSetMetadata&) {
+    return false;
+}
+
+void SyncSourceSelectorMock::setChooseNewSyncSourceResult_forTest(const HostAndPort& syncSource) {
+    _chooseNewSyncSourceResult = syncSource;
+}
+
+OpTime SyncSourceSelectorMock::getChooseNewSyncSourceOpTime_forTest() const {
+    return _chooseNewSyncSourceOpTime;
+}
+
+HostAndPort SyncSourceSelectorMock::getLastBlacklistedSyncSource_forTest() const {
+    return _lastBlacklistedSyncSource;
+}
+
+Date_t SyncSourceSelectorMock::getLastBlacklistExpiration_forTest() const {
+    return _lastBlacklistExpiration;
+}
+
+}  // namespace repl
+}  // namespace mongo
diff --git a/src/mongo/db/repl/sync_source_selector_mock.h b/src/mongo/db/repl/sync_source_selector_mock.h
new file mode 100644
index 00000000000..b53dfb6dd49
--- /dev/null
+++ b/src/mongo/db/repl/sync_source_selector_mock.h
@@ -0,0 +1,99 @@
+/**
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/db/repl/optime.h"
+#include "mongo/db/repl/sync_source_selector.h"
+#include "mongo/stdx/functional.h"
+
+namespace mongo {
+namespace repl {
+
+/**
+ * Mock implementation of SyncSourceSelector interface for testing.
+ */
+class SyncSourceSelectorMock : public SyncSourceSelector {
+    MONGO_DISALLOW_COPYING(SyncSourceSelectorMock);
+
+public:
+    using ChooseNewSyncSourceHook = stdx::function<void()>;
+
+    SyncSourceSelectorMock();
+    virtual ~SyncSourceSelectorMock();
+
+    void clearSyncSourceBlacklist() override;
+    HostAndPort chooseNewSyncSource(const OpTime& ot) override;
+    void blacklistSyncSource(const HostAndPort& host, Date_t until) override;
+    bool shouldChangeSyncSource(const HostAndPort&, const rpc::ReplSetMetadata&) override;
+
+    /**
+     * Sets a function that will be run every time chooseNewSyncSource() is called.
+     */
+    void setChooseNewSyncSourceHook_forTest(const ChooseNewSyncSourceHook& hook);
+
+    /**
+     * Sets the result for subsequent chooseNewSyncSource() invocations.
+     */
+    void setChooseNewSyncSourceResult_forTest(const HostAndPort&);
+
+    /**
+     * Returns most recent optime passed to chooseNewSyncSource().
+     */
+    OpTime getChooseNewSyncSourceOpTime_forTest() const;
+
+    /**
+     * Returns most recently blacklisted sync source.
+     */
+    HostAndPort getLastBlacklistedSyncSource_forTest() const;
+
+    /**
+     * Returns the expiration associated with the most recently blacklisted sync source.
+     */
+    Date_t getLastBlacklistExpiration_forTest() const;
+
+private:
+    // This is the sync source that chooseNewSyncSource returns.
+    HostAndPort _chooseNewSyncSourceResult = HostAndPort("localhost", -1);
+
+    // This is the most recent optime passed to chooseNewSyncSource().
+    OpTime _chooseNewSyncSourceOpTime;
+
+    // This is run every time chooseNewSyncSource() is called.
+    ChooseNewSyncSourceHook _chooseNewSyncSourceHook = []() {};
+
+    // This is the most recently blacklisted sync source passed to blacklistSyncSource().
+    HostAndPort _lastBlacklistedSyncSource;
+
+    // This is the most recent 'util' argument value passed to blacklistSyncSource().
+    Date_t _lastBlacklistExpiration;
+};
+
+}  // namespace repl
+}  // namespace mongo