SERVER-54292 remove dependency on scanning replica set monitor in tenant_migration_recipient_service_tests

9 files changed, 349 insertions, 132 deletions

diff --git a/src/mongo/client/SConscript b/src/mongo/client/SConscript
index e120354b79c..589c74df1af 100644
--- a/src/mongo/client/SConscript
+++ b/src/mongo/client/SConscript
@@ -315,6 +315,18 @@ env.Library(
 )
 
 env.Library(
+    target='replica_set_monitor_test_helper',
+    source=[
+        'streamable_replica_set_monitor_for_testing.cpp',
+    ],
+    LIBDEPS=[
+        '$BUILD_DIR/mongo/client/clientdriver_network',
+        '$BUILD_DIR/mongo/client/sdam/sdam_test',
+        '$BUILD_DIR/mongo/util/net/network',
+    ],
+)
+
+env.Library(
     target='fetcher',
     source=[
         'fetcher.cpp',
diff --git a/src/mongo/client/replica_set_monitor_manager.cpp b/src/mongo/client/replica_set_monitor_manager.cpp
index 0d1d434734e..a21fc832d35 100644
--- a/src/mongo/client/replica_set_monitor_manager.cpp
+++ b/src/mongo/client/replica_set_monitor_manager.cpp
@@ -342,4 +342,10 @@ bool ReplicaSetMonitorManager::isShutdown() const {
 void ReplicaSetMonitorConnectionManager::dropConnections(const HostAndPort& hostAndPort) {
     _network->dropConnections(hostAndPort);
 }
+
+void ReplicaSetMonitorManager::installMonitor_forTests(std::shared_ptr<ReplicaSetMonitor> monitor) {
+    stdx::lock_guard<Latch> lk(_mutex);
+    _monitors[monitor->getName()] = monitor;
+}
+
 }  // namespace mongo
diff --git a/src/mongo/client/replica_set_monitor_manager.h b/src/mongo/client/replica_set_monitor_manager.h
index bde3e41f815..9ce98024c76 100644
--- a/src/mongo/client/replica_set_monitor_manager.h
+++ b/src/mongo/client/replica_set_monitor_manager.h
@@ -156,6 +156,7 @@ public:
 
     bool isShutdown() const;
 
+    void installMonitor_forTests(std::shared_ptr<ReplicaSetMonitor> monitor);
 
 private:
     /**
diff --git a/src/mongo/client/streamable_replica_set_monitor_for_testing.cpp b/src/mongo/client/streamable_replica_set_monitor_for_testing.cpp
new file mode 100644
index 00000000000..e0f582beed6
--- /dev/null
+++ b/src/mongo/client/streamable_replica_set_monitor_for_testing.cpp
@@ -0,0 +1,79 @@
+/**
+ *    Copyright (C) 2021-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    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
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    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 Server Side 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/client/streamable_replica_set_monitor_for_testing.h"
+
+#include "mongo/executor/network_interface_factory.h"
+#include "mongo/executor/network_interface_thread_pool.h"
+#include "mongo/executor/thread_pool_task_executor.h"
+#include "mongo/rpc/metadata/egress_metadata_hook_list.h"
+
+namespace mongo {
+
+StreamableReplicaSetMonitorForTesting::~StreamableReplicaSetMonitorForTesting() {
+    if (_taskExecutor) {
+        _taskExecutor->shutdown();
+        _taskExecutor->join();
+    }
+
+    if (_replSetMonitor) {
+        ReplicaSetMonitorManager::get()->removeMonitor(_replSetMonitor->getName());
+    }
+}
+
+void StreamableReplicaSetMonitorForTesting::setup(const MongoURI& uri) {
+    auto hookList = std::make_unique<rpc::EgressMetadataHookList>();
+    auto networkConnectionHook = std::make_unique<ReplicaSetMonitorManagerNetworkConnectionHook>();
+
+    std::shared_ptr<executor::NetworkInterface> networkInterface =
+        executor::makeNetworkInterface("ReplicaSetMonitor-TestTaskExecutor",
+                                       std::move(networkConnectionHook),
+                                       std::move(hookList));
+    _connectionManager = std::make_unique<ReplicaSetMonitorConnectionManager>(networkInterface);
+
+    auto pool = std::make_unique<executor::NetworkInterfaceThreadPool>(networkInterface.get());
+
+    _taskExecutor =
+        std::make_shared<executor::ThreadPoolTaskExecutor>(std::move(pool), networkInterface);
+    _taskExecutor->startup();
+
+    _replSetMonitor = std::make_shared<StreamableReplicaSetMonitor>(
+        uri, _taskExecutor, _connectionManager, [] {});
+    auto topologyManager = std::make_unique<sdam::MockTopologyManager>();
+    _topologyManagerPtr = topologyManager.get();
+
+    _replSetMonitor->initForTesting(std::move(topologyManager));
+    ReplicaSetMonitorManager::get()->installMonitor_forTests(_replSetMonitor);
+}
+
+sdam::MockTopologyManager* StreamableReplicaSetMonitorForTesting::getTopologyManager() {
+    return _topologyManagerPtr;
+}
+
+}  // namespace mongo
diff --git a/src/mongo/client/streamable_replica_set_monitor_for_testing.h b/src/mongo/client/streamable_replica_set_monitor_for_testing.h
new file mode 100644
index 00000000000..bc481ad735e
--- /dev/null
+++ b/src/mongo/client/streamable_replica_set_monitor_for_testing.h
@@ -0,0 +1,65 @@
+/**
+ *    Copyright (C) 2021-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    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
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    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 Server Side 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/client/replica_set_monitor_manager.h"
+#include "mongo/client/sdam/mock_topology_manager.h"
+#include "mongo/client/streamable_replica_set_monitor.h"
+
+namespace mongo {
+
+/**
+ * Sets up a streamable replica set monitor for testing that does not automatically refresh on its
+ * own, and with configurable topology.
+ */
+class StreamableReplicaSetMonitorForTesting {
+public:
+    ~StreamableReplicaSetMonitorForTesting();
+
+    void setup(const MongoURI& uri);
+
+    sdam::MockTopologyManager* getTopologyManager();
+
+private:
+    // Executor for monitoring replica sets.
+    std::shared_ptr<executor::TaskExecutor> _taskExecutor;
+
+    // Allows closing connections established by the network interface associated with the
+    // _taskExecutor instance
+    std::shared_ptr<ReplicaSetMonitorConnectionManager> _connectionManager;
+
+    // Allows changing replica set topology for mocking replica set targetter response.
+    sdam::MockTopologyManager* _topologyManagerPtr;
+
+    // ReplicaSetMonitorManager only stores weak_ptrs, so we need to keep the monitor alive.
+    std::shared_ptr<StreamableReplicaSetMonitor> _replSetMonitor;
+};
+
+}  // namespace mongo
diff --git a/src/mongo/db/repl/tenant_migration_recipient_service_test.cpp b/src/mongo/db/repl/tenant_migration_recipient_service_test.cpp
index d07efa4226a..554504fce12 100644
--- a/src/mongo/db/repl/tenant_migration_recipient_service_test.cpp
+++ b/src/mongo/db/repl/tenant_migration_recipient_service_test.cpp
@@ -36,6 +36,7 @@
 #include "mongo/client/connpool.h"
 #include "mongo/client/replica_set_monitor.h"
 #include "mongo/client/replica_set_monitor_protocol_test_util.h"
+#include "mongo/client/streamable_replica_set_monitor_for_testing.h"
 #include "mongo/config.h"
 #include "mongo/db/client.h"
 #include "mongo/db/commands/feature_compatibility_version_document_gen.h"
@@ -171,8 +172,10 @@ public:
         ServiceContextMongoDTest::setUp();
         auto serviceContext = getServiceContext();
 
-        // Only the ReplicaSetMonitor scanning protocol supports mock connections.
-        ReplicaSetMonitorProtocolTestUtil::setRSMProtocol(ReplicaSetMonitorProtocol::kScanning);
+        // Fake replSet just for creating consistent URI for monitor
+        MockReplicaSet replSet("donorSet", 1, true /* hasPrimary */, true /* dollarPrefixHosts */);
+        _rsmMonitor.setup(replSet.getURI());
+
         ConnectionString::setConnectionHook(mongo::MockConnRegistry::get()->getConnStrHook());
 
         // Set up clocks.
@@ -402,6 +405,10 @@ protected:
         return instance->_stateDoc;
     }
 
+    sdam::MockTopologyManager* getTopologyManager() {
+        return _rsmMonitor.getTopologyManager();
+    }
+
     /**
      * Advance the time by millis on both clock source mocks.
      */
@@ -445,6 +452,10 @@ protected:
         client->insert(NamespaceString::kServerConfigurationNamespace.ns(), fcvDoc.toBSON());
     }
 
+    ClockSource* clock() {
+        return _clkSource.get();
+    }
+
 private:
     std::shared_ptr<ClockSourceMock> _clkSource = std::make_shared<ClockSourceMock>();
 
@@ -452,6 +463,8 @@ private:
         logv2::LogComponent::kReplication, logv2::LogSeverity::Debug(1)};
     unittest::MinimumLoggedSeverityGuard _tenantMigrationSeverityGuard{
         logv2::LogComponent::kTenantMigration, logv2::LogSeverity::Debug(1)};
+
+    StreamableReplicaSetMonitorForTesting _rsmMonitor;
 };
 
 #ifdef MONGO_CONFIG_SSL
@@ -517,7 +530,7 @@ TEST_F(TenantMigrationRecipientServiceTest, TenantMigrationRecipientConnection_P
     const UUID migrationUUID = UUID::gen();
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -568,7 +581,7 @@ TEST_F(TenantMigrationRecipientServiceTest, TenantMigrationRecipientConnection_S
     const UUID migrationUUID = UUID::gen();
 
     MockReplicaSet replSet("donorSet", 2, true /* hasPrimary */, true /* dollarPrefixHosts */);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -620,7 +633,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
     const UUID migrationUUID = UUID::gen();
 
     MockReplicaSet replSet("donorSet", 2);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -651,25 +664,8 @@ TEST_F(TenantMigrationRecipientServiceTest,
     auto now = opCtx->getServiceContext()->getFastClockSource()->now();
     instance->excludeDonorHost_forTest(hosts.at(0), now + Milliseconds(500));
 
-    AtomicWord<bool> runReplMonitor{true};
-    // Keep scanning the replica set while waiting to reach the failpoint. This would normally
-    // be automatic but that doesn't work with mock replica sets.
-    stdx::thread replMonitorThread([&] {
-        Client::initThread("replMonitorThread");
-        while (runReplMonitor.load()) {
-            auto monitor = ReplicaSetMonitor::get(replSet.getSetName());
-            // Monitor may not have been created yet.
-            if (monitor) {
-                monitor->runScanForMockReplicaSet();
-            }
-            mongo::sleepmillis(100);
-        }
-    });
-
     hangFp->setMode(FailPoint::off);
     taskFp->waitForTimesEntered(taskFpInitialTimesEntered + 1);
-    runReplMonitor.store(false);
-    replMonitorThread.join();
 
     auto* client = getClient(instance.get());
     auto* oplogFetcherClient = getOplogFetcherClient(instance.get());
@@ -695,7 +691,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
     const UUID migrationUUID = UUID::gen();
 
     MockReplicaSet replSet("donorSet", 2);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -767,7 +763,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
     const UUID migrationUUID = UUID::gen();
 
     MockReplicaSet replSet("donorSet", 2);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -801,25 +797,8 @@ TEST_F(TenantMigrationRecipientServiceTest,
         instance->excludeDonorHost_forTest(host, now + Milliseconds(500));
     }
 
-    AtomicWord<bool> runReplMonitor{true};
-    // Keep scanning the replica set while waiting to reach the failpoint. This would normally
-    // be automatic but that doesn't work with mock replica sets.
-    stdx::thread replMonitorThread([&] {
-        Client::initThread("replMonitorThread");
-        while (runReplMonitor.load()) {
-            auto monitor = ReplicaSetMonitor::get(replSet.getSetName());
-            // Monitor may not have been created yet.
-            if (monitor) {
-                monitor->runScanForMockReplicaSet();
-            }
-            mongo::sleepmillis(100);
-        }
-    });
-
     hangFp->setMode(FailPoint::off);
     taskFp->waitForTimesEntered(taskFpInitialTimesEntered + 1);
-    runReplMonitor.store(false);
-    replMonitorThread.join();
 
     auto* client = getClient(instance.get());
     auto* oplogFetcherClient = getOplogFetcherClient(instance.get());
@@ -845,7 +824,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
     const UUID migrationUUID = UUID::gen();
 
     MockReplicaSet replSet("donorSet", 2);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -914,7 +893,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
     const UUID migrationUUID = UUID::gen();
 
     MockReplicaSet replSet("donorSet", 2);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -986,7 +965,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
     const UUID migrationUUID = UUID::gen();
 
     MockReplicaSet replSet("donorSet", 3);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -1018,26 +997,10 @@ TEST_F(TenantMigrationRecipientServiceTest,
     auto now = opCtx->getServiceContext()->getFastClockSource()->now();
     auto excludeTime = Milliseconds(500);
     instance->excludeDonorHost_forTest(hosts.at(2), now + excludeTime);
-
-    AtomicWord<bool> runReplMonitor{true};
-    // Keep scanning the replica set while waiting to reach the failpoint. This would normally
-    // be automatic but that doesn't work with mock replica sets.
-    stdx::thread replMonitorThread([&] {
-        Client::initThread("replMonitorThread");
-        while (runReplMonitor.load()) {
-            auto monitor = ReplicaSetMonitor::get(replSet.getSetName());
-            // Monitor may not have been created yet.
-            if (monitor) {
-                monitor->runScanForMockReplicaSet();
-            }
-            mongo::sleepmillis(100);
-        }
-    });
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
 
     hangFp->setMode(FailPoint::off);
     taskFp->waitForTimesEntered(taskFpInitialTimesEntered + 1);
-    runReplMonitor.store(false);
-    replMonitorThread.join();
 
     auto* client = getClient(instance.get());
     auto* oplogFetcherClient = getOplogFetcherClient(instance.get());
@@ -1063,7 +1026,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
     const UUID migrationUUID = UUID::gen();
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -1096,6 +1059,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
     auto now = opCtx->getServiceContext()->getFastClockSource()->now();
     auto excludeTime = Milliseconds(500);
     instance->excludeDonorHost_forTest(hosts.at(2), now + excludeTime);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
 
     hangFp->setMode(FailPoint::off);
     taskFp->waitForTimesEntered(taskFpInitialTimesEntered + 1);
@@ -1136,6 +1100,8 @@ TEST_F(TenantMigrationRecipientServiceTest,
 
     // Insert the remote majority optime into the oplogs of the first two hosts.
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
+
     const auto hosts = replSet.getHosts();
     const std::vector<HostAndPort> advancedOpTimeHosts = {hosts.begin(), hosts.begin() + 2};
 
@@ -1192,6 +1158,8 @@ TEST_F(TenantMigrationRecipientServiceTest,
 
     // Insert the remote majority optime into the oplogs of the first two hosts.
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
+
     const auto hosts = replSet.getHosts();
     const std::vector<HostAndPort> advancedOpTimeHosts = {hosts[0], hosts[1]};
 
@@ -1252,11 +1220,12 @@ TEST_F(TenantMigrationRecipientServiceTest, TenantMigrationRecipientConnection_P
     const UUID migrationUUID = UUID::gen();
 
     MockReplicaSet replSet("donorSet", 2, true /* hasPrimary */, true /* dollarPrefixHosts */);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     // Primary is unavailable.
     replSet.kill(replSet.getHosts()[0].toString());
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
 
     TenantMigrationRecipientDocument initialStateDocument(
         migrationUUID,
@@ -1347,6 +1316,7 @@ TEST_F(TenantMigrationRecipientServiceTest, TenantMigrationRecipientGetStartOpTi
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -1385,6 +1355,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
     const OpTime newTopOfOplogOpTime(Timestamp(6, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -1423,7 +1394,9 @@ TEST_F(TenantMigrationRecipientServiceTest, TenantMigrationRecipientGetStartOpTi
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
+
     SessionTxnRecord lastTxn(makeLogicalSessionIdForTest(), 100, txnLastWriteOpTime, Date_t());
     lastTxn.setStartOpTime(txnStartOpTime);
     lastTxn.setState(DurableTxnStateEnum::kInProgress);
@@ -1468,7 +1441,9 @@ TEST_F(TenantMigrationRecipientServiceTest,
     const OpTime newTopOfOplogOpTime(Timestamp(6, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
+
     SessionTxnRecord lastTxn(makeLogicalSessionIdForTest(), 100, txnLastWriteOpTime, Date_t());
     lastTxn.setStartOpTime(txnStartOpTime);
     lastTxn.setState(DurableTxnStateEnum::kInProgress);
@@ -1509,6 +1484,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
     const UUID migrationUUID = UUID::gen();
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
 
     TenantMigrationRecipientDocument initialStateDocument(
         migrationUUID,
@@ -1542,6 +1518,7 @@ TEST_F(TenantMigrationRecipientServiceTest, TenantMigrationRecipientStartOplogFe
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -1590,6 +1567,7 @@ TEST_F(TenantMigrationRecipientServiceTest, TenantMigrationRecipientStartsCloner
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     // Skip the cloners in this test, so we provide an empty list of databases.
@@ -1650,6 +1628,7 @@ TEST_F(TenantMigrationRecipientServiceTest, OplogFetcherFailsDuringOplogApplicat
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -1705,6 +1684,7 @@ TEST_F(TenantMigrationRecipientServiceTest, OplogFetcherResumesFromTopOfOplogBuf
     const OpTime dataConsistentOpTime(Timestamp(4, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, initialOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -1811,6 +1791,7 @@ TEST_F(TenantMigrationRecipientServiceTest, OplogFetcherNoDocInBufferToResumeFro
     const OpTime dataConsistentOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, startFetchingOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -1919,6 +1900,7 @@ TEST_F(TenantMigrationRecipientServiceTest, OplogApplierResumesFromLastNoOpOplog
     const OpTime dataConsistentOpTime(Timestamp(4, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, clonerFinishedOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -2043,6 +2025,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
     const OpTime dataConsistentOpTime(Timestamp(4, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, startApplyingOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -2207,6 +2190,7 @@ TEST_F(TenantMigrationRecipientServiceTest, OplogApplierResumesFromStartDonorApp
     const OpTime dataConsistentOpTime(Timestamp(4, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, startApplyingOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -2351,6 +2335,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
     const OpTime dataConsistentOpTime(Timestamp(4, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, startFetchingOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -2456,6 +2441,7 @@ TEST_F(TenantMigrationRecipientServiceTest, OplogApplierFails) {
     const OpTime injectedEntryOpTime(Timestamp(6, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -2521,6 +2507,7 @@ TEST_F(TenantMigrationRecipientServiceTest, StoppingApplierAllowsCompletion) {
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -2575,6 +2562,7 @@ TEST_F(TenantMigrationRecipientServiceTest, TenantMigrationRecipientAddResumeTok
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /*dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -2678,6 +2666,8 @@ TEST_F(TenantMigrationRecipientServiceTest, TenantMigrationRecipientAddResumeTok
 TEST_F(TenantMigrationRecipientServiceTest, RecipientForgetMigration_BeforeRun) {
     const UUID migrationUUID = UUID::gen();
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
+
     TenantMigrationRecipientDocument initialStateDocument(
         migrationUUID,
         replSet.getConnectionString(),
@@ -2714,6 +2704,8 @@ TEST_F(TenantMigrationRecipientServiceTest, RecipientForgetMigration_FailToIniti
 
     const UUID migrationUUID = UUID::gen();
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
+
     TenantMigrationRecipientDocument initialStateDocument(
         migrationUUID,
         replSet.getConnectionString(),
@@ -2745,6 +2737,7 @@ TEST_F(TenantMigrationRecipientServiceTest, RecipientForgetMigration_WaitUntilSt
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -2828,6 +2821,7 @@ TEST_F(TenantMigrationRecipientServiceTest, RecipientForgetMigration_AfterStartO
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -2890,6 +2884,7 @@ TEST_F(TenantMigrationRecipientServiceTest, RecipientForgetMigration_AfterConsis
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -2977,6 +2972,7 @@ TEST_F(TenantMigrationRecipientServiceTest, RecipientForgetMigration_AfterFail)
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -3059,6 +3055,8 @@ TEST_F(TenantMigrationRecipientServiceTest, RecipientForgetMigration_FailToMarkG
     const UUID migrationUUID = UUID::gen();
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
+
     TenantMigrationRecipientDocument initialStateDocument(
         migrationUUID,
         replSet.getConnectionString(),
@@ -3108,7 +3106,7 @@ TEST_F(TenantMigrationRecipientServiceTest, TenantMigrationRecipientServiceRecor
 
     const UUID migrationUUID = UUID::gen();
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -3143,7 +3141,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
 
     const UUID migrationUUID = UUID::gen();
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -3182,7 +3180,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
 
     const UUID migrationUUID = UUID::gen();
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -3230,7 +3228,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
 
     const UUID migrationUUID = UUID::gen();
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
-
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, OpTime(kDefaultStartMigrationTimestamp, 1));
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -3265,6 +3263,7 @@ TEST_F(TenantMigrationRecipientServiceTest, WaitUntilMigrationReachesReturnAfter
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -3324,6 +3323,7 @@ TEST_F(TenantMigrationRecipientServiceTest, RecipientReceivesRetriableFetcherErr
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -3387,6 +3387,7 @@ TEST_F(TenantMigrationRecipientServiceTest, RecipientReceivesNonRetriableFetcher
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -3445,6 +3446,7 @@ TEST_F(TenantMigrationRecipientServiceTest, RecipientWillNotRetryOnExternalInter
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -3502,6 +3504,7 @@ TEST_F(TenantMigrationRecipientServiceTest, RecipientReceivesRetriableClonerErro
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -3567,6 +3570,7 @@ TEST_F(TenantMigrationRecipientServiceTest, RecipientReceivesNonRetriableClonerE
     const OpTime topOfOplogOpTime(Timestamp(5, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -3614,6 +3618,7 @@ TEST_F(TenantMigrationRecipientServiceTest, IncrementNumRestartsDueToRecipientFa
     const OpTime topOfOplogOpTime(Timestamp(1, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
@@ -3664,6 +3669,7 @@ TEST_F(TenantMigrationRecipientServiceTest,
     const OpTime topOfOplogOpTime(Timestamp(1, 1), 1);
 
     MockReplicaSet replSet("donorSet", 3, true /* hasPrimary */, true /* dollarPrefixHosts */);
+    getTopologyManager()->setTopologyDescription(replSet.getTopologyDescription(clock()));
     insertTopOfOplog(&replSet, topOfOplogOpTime);
 
     TenantMigrationRecipientDocument initialStateDocument(
diff --git a/src/mongo/dbtests/SConscript b/src/mongo/dbtests/SConscript
index a6f5f42328b..09bc1e576d3 100644
--- a/src/mongo/dbtests/SConscript
+++ b/src/mongo/dbtests/SConscript
@@ -57,6 +57,7 @@ env.Library(
     LIBDEPS=[
         '$BUILD_DIR/mongo/client/clientdriver_network',
         '$BUILD_DIR/mongo/client/dbclient_mockcursor',
+        '$BUILD_DIR/mongo/client/replica_set_monitor_test_helper',
         '$BUILD_DIR/mongo/db/repl/replica_set_messages'
     ],
     LIBDEPS_PRIVATE=[
diff --git a/src/mongo/dbtests/mock/mock_replica_set.cpp b/src/mongo/dbtests/mock/mock_replica_set.cpp
index 358c880de45..add43163b36 100644
--- a/src/mongo/dbtests/mock/mock_replica_set.cpp
+++ b/src/mongo/dbtests/mock/mock_replica_set.cpp
@@ -31,6 +31,7 @@
 
 #include "mongo/dbtests/mock/mock_replica_set.h"
 
+#include "mongo/client/sdam/topology_description_builder.h"
 #include "mongo/db/repl/member_state.h"
 #include "mongo/dbtests/mock/mock_conn_registry.h"
 #include "mongo/dbtests/mock/mock_dbclient_connection.h"
@@ -199,90 +200,96 @@ void MockReplicaSet::restore(const string& hostAndPort) {
     _nodeMap[hostAndPort]->reboot();
 }
 
-void MockReplicaSet::mockIsMasterCmd() {
-    for (ReplNodeMap::iterator nodeIter = _nodeMap.begin(); nodeIter != _nodeMap.end();
-         ++nodeIter) {
-        const string& hostAndPort = nodeIter->first;
+BSONObj MockReplicaSet::mockHelloResponseFor(const MockRemoteDBServer& server) const {
+    const auto hostAndPort = server.getServerHostAndPort();
 
-        BSONObjBuilder builder;
-        builder.append("setName", _setName);
+    BSONObjBuilder builder;
+    builder.append("setName", _setName);
 
-        const MemberConfig* member = _replConfig.findMemberByHostAndPort(HostAndPort(hostAndPort));
-        if (!member) {
-            builder.append("ismaster", false);
-            builder.append("secondary", false);
+    const MemberConfig* member = _replConfig.findMemberByHostAndPort(hostAndPort);
+    if (!member) {
+        builder.append("ismaster", false);
+        builder.append("secondary", false);
 
-            vector<string> hostList;
-            builder.append("hosts", hostList);
-        } else {
-            const bool isPrimary = hostAndPort == getPrimary();
-            builder.append("ismaster", isPrimary);
-            builder.append("secondary", !isPrimary);
-
-            {
-                // TODO: add passives & arbiters
-                vector<string> hostList;
-                if (hasPrimary()) {
-                    hostList.push_back(getPrimary());
-                }
-
-                const vector<string> secondaries = getSecondaries();
-                for (vector<string>::const_iterator secIter = secondaries.begin();
-                     secIter != secondaries.end();
-                     ++secIter) {
-                    hostList.push_back(*secIter);
-                }
-
-                builder.append("hosts", hostList);
-            }
+        vector<string> hostList;
+        builder.append("hosts", hostList);
+    } else {
+        const bool isPrimary = hostAndPort.toString() == getPrimary();
+        builder.append("ismaster", isPrimary);
+        builder.append("secondary", !isPrimary);
 
+        {
+            // TODO: add passives & arbiters
+            vector<string> hostList;
             if (hasPrimary()) {
-                builder.append("primary", getPrimary());
+                hostList.push_back(getPrimary());
             }
 
-            if (member->isArbiter()) {
-                builder.append("arbiterOnly", true);
+            const vector<string> secondaries = getSecondaries();
+            for (vector<string>::const_iterator secIter = secondaries.begin();
+                 secIter != secondaries.end();
+                 ++secIter) {
+                hostList.push_back(*secIter);
             }
 
-            if (member->getPriority() == 0 && !member->isArbiter()) {
-                builder.append("passive", true);
-            }
+            builder.append("hosts", hostList);
+        }
 
-            if (member->getSecondaryDelay().count()) {
-                builder.appendNumber("secondaryDelaySecs",
-                                     durationCount<Seconds>(member->getSecondaryDelay()));
-            }
+        if (hasPrimary()) {
+            builder.append("primary", getPrimary());
+        }
 
-            if (member->isHidden()) {
-                builder.append("hidden", true);
-            }
+        if (member->isArbiter()) {
+            builder.append("arbiterOnly", true);
+        }
 
-            if (!member->shouldBuildIndexes()) {
-                builder.append("buildIndexes", false);
-            }
+        if (member->getPriority() == 0 && !member->isArbiter()) {
+            builder.append("passive", true);
+        }
+
+        if (member->getSecondaryDelay().count()) {
+            builder.appendNumber("secondaryDelaySecs",
+                                 durationCount<Seconds>(member->getSecondaryDelay()));
+        }
 
-            const ReplSetTagConfig tagConfig = _replConfig.getTagConfig();
-            if (member->hasTags()) {
-                BSONObjBuilder tagBuilder;
-                for (MemberConfig::TagIterator tag = member->tagsBegin(); tag != member->tagsEnd();
-                     ++tag) {
-                    std::string tagKey = tagConfig.getTagKey(*tag);
-                    if (tagKey[0] == '$') {
-                        // Filter out internal tags
-                        continue;
-                    }
-                    tagBuilder.append(tagKey, tagConfig.getTagValue(*tag));
+        if (member->isHidden()) {
+            builder.append("hidden", true);
+        }
+
+        if (!member->shouldBuildIndexes()) {
+            builder.append("buildIndexes", false);
+        }
+
+        const ReplSetTagConfig tagConfig = _replConfig.getTagConfig();
+        if (member->hasTags()) {
+            BSONObjBuilder tagBuilder;
+            for (MemberConfig::TagIterator tag = member->tagsBegin(); tag != member->tagsEnd();
+                 ++tag) {
+                std::string tagKey = tagConfig.getTagKey(*tag);
+                if (tagKey[0] == '$') {
+                    // Filter out internal tags
+                    continue;
                 }
-                builder.append("tags", tagBuilder.done());
+                tagBuilder.append(tagKey, tagConfig.getTagValue(*tag));
             }
+            builder.append("tags", tagBuilder.done());
         }
+    }
 
-        builder.append("me", hostAndPort);
-        builder.append("ok", true);
+    builder.append("me", hostAndPort.toString());
+    builder.append("ok", 1);
+
+    return builder.obj();
+}
+
+void MockReplicaSet::mockIsMasterCmd() {
+    for (ReplNodeMap::iterator nodeIter = _nodeMap.begin(); nodeIter != _nodeMap.end();
+         ++nodeIter) {
+        auto isMaster = mockHelloResponseFor(*nodeIter->second);
 
         // DBClientBase::isMaster() sends "ismaster", but ReplicaSetMonitor sends "isMaster".
-        nodeIter->second->setCommandReply("ismaster", builder.done());
-        nodeIter->second->setCommandReply("isMaster", builder.done());
+        nodeIter->second->setCommandReply("ismaster", isMaster);
+        nodeIter->second->setCommandReply("isMaster", isMaster);
     }
 }
 
@@ -354,4 +361,30 @@ void MockReplicaSet::mockReplSetGetStatusCmd() {
         node->setCommandReply("replSetGetStatus", fullStatBuilder.done());
     }
 }
+
+sdam::TopologyDescriptionPtr MockReplicaSet::getTopologyDescription(
+    ClockSource* clockSource) const {
+    sdam::TopologyDescriptionBuilder builder;
+
+    builder.withSetName(_setName);
+    builder.withTopologyType(hasPrimary() ? sdam::TopologyType::kReplicaSetWithPrimary
+                                          : sdam::TopologyType::kReplicaSetNoPrimary);
+
+    std::vector<sdam::ServerDescriptionPtr> servers;
+    for (const auto& nodeEntry : _nodeMap) {
+        const auto& server = *nodeEntry.second;
+        if (server.isRunning()) {
+            auto helloBSON = mockHelloResponseFor(server);
+            sdam::HelloOutcome hello(server.getServerHostAndPort(), helloBSON);
+            servers.push_back(std::make_shared<sdam::ServerDescription>(clockSource, hello));
+        } else {
+            sdam::HelloOutcome hello(server.getServerHostAndPort(), {}, "mock server unreachable");
+            servers.push_back(std::make_shared<sdam::ServerDescription>(clockSource, hello));
+        }
+    }
+
+    builder.withServers(servers);
+    return builder.instance();
+}
+
 }  // namespace mongo
diff --git a/src/mongo/dbtests/mock/mock_replica_set.h b/src/mongo/dbtests/mock/mock_replica_set.h
index 01929b0e203..7d87afce62a 100644
--- a/src/mongo/dbtests/mock/mock_replica_set.h
+++ b/src/mongo/dbtests/mock/mock_replica_set.h
@@ -29,6 +29,7 @@
 
 #pragma once
 
+#include "mongo/client/sdam/sdam_datatypes.h"
 #include "mongo/db/repl/member_config.h"
 #include "mongo/db/repl/repl_set_config.h"
 #include "mongo/dbtests/mock/mock_remote_db_server.h"
@@ -38,6 +39,9 @@
 #include <vector>
 
 namespace mongo {
+
+class ClockSource;
+
 /**
  * This is a helper class for managing a replica set consisting of
  * MockRemoteDBServer instances.
@@ -124,6 +128,11 @@ public:
      */
     void restore(const std::string& hostName);
 
+    /**
+     * Returns a topology description reflecting the current state of this replica set.
+     */
+    sdam::TopologyDescriptionPtr getTopologyDescription(ClockSource* clockSource) const;
+
 private:
     typedef std::map<std::string, MockRemoteDBServer*> ReplNodeMap;
 
@@ -134,6 +143,11 @@ private:
     void mockIsMasterCmd();
 
     /**
+     * Mock the hello response for the given server.
+     */
+    BSONObj mockHelloResponseFor(const MockRemoteDBServer& server) const;
+
+    /**
      * Mocks the replSetGetStatus command based on the current states of the
      * mocked servers.
      */