SERVER-9174 Race condition on read_pref_rs_client.js after reconfig

Replaced js test with cpp unit test that does not rely on reconfig.

4 files changed, 385 insertions, 252 deletions

diff --git a/jstests/sharding/read_pref_rs_client.js b/jstests/sharding/read_pref_rs_client.js
deleted file mode 100644
index 8a458101aa2..00000000000
--- a/jstests/sharding/read_pref_rs_client.js
+++ /dev/null
@@ -1,220 +0,0 @@
-/**
- * Testing read preference on DBClientReplicaSets, specifically on the auto-retry
- * and automatic failover selection
- */
-// NOTE: this test is skipped when running smoke.py with --auth because of SERVER-6972
-
-function basicTest() {
-    var replTest = new ReplSetTest({ name: 'basic', nodes: 2, useHostName: true });
-    replTest.startSet({ oplogSize: 1 });
-    replTest.initiate();
-    replTest.awaitSecondaryNodes();
-
-    var PRI_HOST = replTest.getPrimary().host;
-    var SEC_HOST = replTest.getSecondary().host;
-
-    var replConn = new Mongo(replTest.getURL());
-    var coll = replConn.getDB('test').user;
-    var dest = coll.find().readPref('primary').explain().server;
-    assert.eq(PRI_HOST, dest);
-
-    // Create brand new connection to make sure that the last cached is not used
-    replConn = new Mongo(replTest.getURL());
-    coll = replConn.getDB('test').user;
-    dest = coll.find().readPref('secondary').explain().server;
-    assert.eq(SEC_HOST, dest);
-
-    replConn = new Mongo(replTest.getURL());
-    coll = replConn.getDB('test').user;
-    dest = coll.find().readPref('primaryPreferred').explain().server;
-    assert.eq(PRI_HOST, dest);
-
-    replConn = new Mongo(replTest.getURL());
-    coll = replConn.getDB('test').user;
-    dest = coll.find().readPref('secondaryPreferred').explain().server;
-    assert.eq(SEC_HOST, dest);
-
-    replConn = new Mongo(replTest.getURL());
-    coll = replConn.getDB('test').user;
-    // just make sure that it doesn't throw
-    coll.find().readPref('nearest').explain();
-
-    replTest.stopSet();
-}
-
-function noPriNoSecTest() {
-    var replTest = new ReplSetTest({ name: 'noPriNoSec', useHostName: true,
-        nodes: [{}, { arbiter: true }, { arbiter: true }]});
-    replTest.startSet({ oplogSize: 1 });
-    replTest.initiate();
-    replTest.awaitSecondaryNodes();
-
-    var replConn = new Mongo(replTest.getURL());
-    var coll = replConn.getDB('test').user;
-
-    replTest.stop(0);
-
-    assert.throws(function() {
-        coll.find().readPref('primary').explain();
-    });
-
-    // Make sure that it still fails even when trying to refresh
-    assert.throws(function() {
-        coll.find().readPref('primary').explain();
-    });
-
-    // Don't need to create new connection because failed connections
-    // would never be reused, and also becasue the js Mongo contructor
-    // will throw when it can't connect to a primary
-    assert.throws(function() {
-        coll.find().readPref('secondary').explain();
-    });
-
-    assert.throws(function() {
-        coll.find().readPref('secondary').explain();
-    });
-
-    assert.throws(function() {
-        coll.find().readPref('primaryPreferred').explain();
-    });
-
-    assert.throws(function() {
-        coll.find().readPref('primaryPreferred').explain();
-    });
-
-    assert.throws(function() {
-        coll.find().readPref('secondaryPreferred').explain();
-    });
-
-    assert.throws(function() {
-        coll.find().readPref('secondaryPreferred').explain();
-    });
-
-    assert.throws(function() {
-        coll.find().readPref('neareset').explain();
-    });
-
-    assert.throws(function() {
-        coll.find().readPref('nearest').explain();
-    });
-
-    replTest.stopSet();
-}
-
-function priOkNoSecTest() {
-    var replTest = new ReplSetTest({ name: 'priOkNoSec', useHostName: true,
-        nodes: [{}, { arbiter: true }, {}]});
-    replTest.startSet({ oplogSize: 1 });
-    replTest.initiate();
-    replTest.awaitSecondaryNodes();
-
-    var replConn = new Mongo(replTest.getURL());
-    var coll = replConn.getDB('test').user;
-
-    replTest.stop(2);
-
-    var PRI_HOST = replTest.getPrimary().host;
-
-    var dest = coll.find().readPref('primary').explain().server;
-    assert.eq(PRI_HOST, dest);
-
-    replConn = new Mongo(replTest.getURL());
-    coll = replConn.getDB('test').user;
-    dest = coll.find().readPref('primaryPreferred').explain().server;
-    assert.eq(PRI_HOST, dest);
-
-    replConn = new Mongo(replTest.getURL());
-    coll = replConn.getDB('test').user;
-    assert.throws(function() {
-        coll.find().readPref('secondary').explain();
-    });
-
-    assert.throws(function() {
-        coll.find().readPref('secondary').explain();
-    });
-
-    replConn = new Mongo(replTest.getURL());
-    coll = replConn.getDB('test').user;
-    dest = coll.find().readPref('secondaryPreferred').explain().server;
-    assert.eq(PRI_HOST, dest);
-
-    replConn = new Mongo(replTest.getURL());
-    coll = replConn.getDB('test').user;
-    dest = coll.find().readPref('nearest').explain().server;
-    assert.eq(PRI_HOST, dest);
-
-    replTest.stopSet();
-}
-
-function noPriSecOkTest() {
-    var replTest = new ReplSetTest({ name: 'noPriSecOk', useHostName: true,
-        nodes: [{ }, { arbiter: true }, { }]});
-    replTest.startSet({ oplogSize: 1 });
-    replTest.initiate();
-    replTest.awaitSecondaryNodes();
-
-    var priConn = replTest.getPrimary();
-    var conf = priConn.getDB('local').system.replset.findOne();
-    conf.version++;
-    conf.members[0].priority = 99;
-    conf.members[2].priority = 0;
-
-    var SEC_HOST = replTest.nodes[2].host;
-
-    try {
-        priConn.getDB('admin').runCommand({ replSetReconfig: conf });
-    } catch (x) {
-        print('Exception from reconfig: ' + x);
-    }
-
-    var replConn = new Mongo(replTest.getURL());
-    var coll = replConn.getDB('test').user;
-
-    replTest.stop(0);
-
-    assert.throws(function() {
-        coll.find().readPref('primary').explain();
-    });
-
-    // Make sure that it still fails even when trying to refresh
-    assert.throws(function() {
-        coll.find().readPref('primary').explain();
-    });
-
-    replConn = new Mongo(replTest.getURL());
-    coll = replConn.getDB('test').user;
-    var dest = coll.find().readPref('primaryPreferred').explain().server;
-    assert.eq(SEC_HOST, dest);
-
-    replTest.start(0, {}, true);
-    replTest.awaitSecondaryNodes();
-    replConn = new Mongo(replTest.getURL());
-    replTest.stop(0);
-    coll = replConn.getDB('test').user;
-    dest = coll.find().readPref('secondary').explain().server;
-    assert.eq(SEC_HOST, dest);
-
-    replTest.start(0, {}, true);
-    replTest.awaitSecondaryNodes();
-    replConn = new Mongo(replTest.getURL());
-    replTest.stop(0);
-    coll = replConn.getDB('test').user;
-    dest = coll.find().readPref('secondaryPreferred').explain().server;
-    assert.eq(SEC_HOST, dest);
-
-    replTest.start(0, {}, true);
-    replTest.awaitSecondaryNodes();
-    replConn = new Mongo(replTest.getURL());
-    replTest.stop(0);
-    coll = replConn.getDB('test').user;
-    dest = coll.find().readPref('nearest').explain().server;
-    assert.eq(SEC_HOST, dest);
-
-    replTest.stopSet();
-}
-
-basicTest();
-noPriNoSecTest();
-priOkNoSecTest();
-noPriSecOkTest();
-
diff --git a/src/mongo/client/dbclient_rs_test.cpp b/src/mongo/client/dbclient_rs_test.cpp
index 19e94a0fc9f..ccb7b71063e 100644
--- a/src/mongo/client/dbclient_rs_test.cpp
+++ b/src/mongo/client/dbclient_rs_test.cpp
@@ -15,7 +15,8 @@
  */
 
 /**
- * This file contains tests for DBClientReplicaSet.
+ * This file contains tests for DBClientReplicaSet. The tests mocks the servers
+ * the DBClientReplicaSet talks to, so the tests only covers the client side logic.
  */
 
 #include "mongo/bson/bson_field.h"
@@ -25,35 +26,13 @@
 #include "mongo/dbtests/mock/mock_conn_registry.h"
 #include "mongo/dbtests/mock/mock_replica_set.h"
 #include "mongo/unittest/unittest.h"
+#include "mongo/util/assert_util.h"
 
 #include <map>
 #include <memory>
 #include <string>
 #include <vector>
 
-using std::auto_ptr;
-using std::map;
-using std::make_pair;
-using std::pair;
-using std::string;
-using std::vector;
-using boost::scoped_ptr;
-
-using mongo::BSONField;
-using mongo::BSONObj;
-using mongo::BSONArray;
-using mongo::BSONElement;
-using mongo::ConnectionString;
-using mongo::DBClientCursor;
-using mongo::DBClientReplicaSet;
-using mongo::HostAndPort;
-using mongo::MockReplicaSet;
-using mongo::Query;
-using mongo::ReadPreference;
-using mongo::ReplicaSetMonitor;
-using mongo::ScopedDbConnection;
-using mongo::TagSet;
-
 namespace mongo {
     // Symbols defined to build the binary correctly.
     CmdLine cmdLine;
@@ -73,16 +52,373 @@ namespace mongo {
     }
 }
 
-namespace mongo_test {
+namespace {
+    using boost::scoped_ptr;
+    using std::auto_ptr;
+    using std::map;
+    using std::make_pair;
+    using std::pair;
+    using std::string;
+    using std::vector;
+
+    using mongo::AssertionException;
+    using mongo::BSONArray;
+    using mongo::BSONElement;
+    using mongo::BSONField;
+    using mongo::BSONObj;
+    using mongo::ConnectionString;
+    using mongo::DBClientCursor;
+    using mongo::DBClientReplicaSet;
+    using mongo::HostAndPort;
+    using mongo::HostField;
+    using mongo::IdentityNS;
+    using mongo::MockReplicaSet;
+    using mongo::Query;
+    using mongo::ReadPreference;
+    using mongo::ReplicaSetMonitor;
+    using mongo::ScopedDbConnection;
+    using mongo::TagSet;
+
+    /**
+     * Basic fixture with one primary and one secondary.
+     */
+    class BasicRS: public mongo::unittest::Test {
+    protected:
+        void setUp() {
+            _replSet.reset(new MockReplicaSet("test", 2));
+            ConnectionString::setConnectionHook(
+                    mongo::MockConnRegistry::get()->getConnStrHook());
+        }
+
+        void tearDown() {
+            ReplicaSetMonitor::remove(_replSet->getSetName(), true);
+            _replSet.reset();
+
+            // TODO: remove this after we remove replSetGetStatus from ReplicaSetMonitor.
+            mongo::ScopedDbConnection::clearPool();
+        }
+
+        MockReplicaSet* getReplSet() {
+            return _replSet.get();
+        }
+
+    private:
+        boost::scoped_ptr<MockReplicaSet> _replSet;
+    };
+
+    TEST_F(BasicRS, ReadFromPrimary) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_PrimaryOnly, BSONArray());
+
+        // Note: IdentityNS contains the name of the server.
+        auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
+        BSONObj doc = cursor->next();
+        ASSERT_EQUALS(replSet->getPrimary(), doc[HostField.name()].str());
+    }
+
+    TEST_F(BasicRS, SecondaryOnly) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_SecondaryOnly, BSONArray());
+
+        // Note: IdentityNS contains the name of the server.
+        auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
+        BSONObj doc = cursor->next();
+        ASSERT_EQUALS(replSet->getSecondaries().front(), doc[HostField.name()].str());
+    }
+
+    TEST_F(BasicRS, PrimaryPreferred) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_PrimaryPreferred, BSONArray());
+
+        // Note: IdentityNS contains the name of the server.
+        auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
+        BSONObj doc = cursor->next();
+        ASSERT_EQUALS(replSet->getPrimary(), doc[HostField.name()].str());
+    }
+
+    TEST_F(BasicRS, SecondaryPreferred) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_SecondaryPreferred, BSONArray());
+
+        // Note: IdentityNS contains the name of the server.
+        auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
+        BSONObj doc = cursor->next();
+        ASSERT_EQUALS(replSet->getSecondaries().front(), doc[HostField.name()].str());
+    }
+
+    /**
+     * Setup for 2 member replica set will all of the nodes down.
+     */
+    class AllNodesDown: public mongo::unittest::Test {
+    protected:
+        void setUp() {
+            _replSet.reset(new MockReplicaSet("test", 2));
+            ConnectionString::setConnectionHook(
+                    mongo::MockConnRegistry::get()->getConnStrHook());
+
+            vector<HostAndPort> hostList(_replSet->getHosts());
+            for (vector<HostAndPort>::const_iterator iter = hostList.begin();
+                    iter != hostList.end(); ++iter) {
+                _replSet->kill(iter->toString(true));
+            }
+        }
+
+        void tearDown() {
+            ReplicaSetMonitor::remove(_replSet->getSetName(), true);
+            _replSet.reset();
+
+            // TODO: remove this after we remove replSetGetStatus from ReplicaSetMonitor.
+            mongo::ScopedDbConnection::clearPool();
+        }
+
+        MockReplicaSet* getReplSet() {
+            return _replSet.get();
+        }
+
+    private:
+        boost::scoped_ptr<MockReplicaSet> _replSet;
+    };
+
+    TEST_F(AllNodesDown, ReadFromPrimary) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_PrimaryOnly, BSONArray());
+        ASSERT_THROWS(replConn.query(IdentityNS, query), AssertionException);
+    }
+
+    TEST_F(AllNodesDown, SecondaryOnly) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_SecondaryOnly, BSONArray());
+        ASSERT_THROWS(replConn.query(IdentityNS, query), AssertionException);
+    }
+
+    TEST_F(AllNodesDown, PrimaryPreferred) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_PrimaryPreferred, BSONArray());
+        ASSERT_THROWS(replConn.query(IdentityNS, query), AssertionException);
+    }
+
+    TEST_F(AllNodesDown, SecondaryPreferred) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_SecondaryPreferred, BSONArray());
+        ASSERT_THROWS(replConn.query(IdentityNS, query), AssertionException);
+    }
+
+    TEST_F(AllNodesDown, Nearest) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_Nearest, BSONArray());
+        ASSERT_THROWS(replConn.query(IdentityNS, query), AssertionException);
+    }
+
+    /**
+     * Setup for 2 member replica set with the primary down.
+     */
+    class PrimaryDown: public mongo::unittest::Test {
+    protected:
+        void setUp() {
+            _replSet.reset(new MockReplicaSet("test", 2));
+            ConnectionString::setConnectionHook(
+                    mongo::MockConnRegistry::get()->getConnStrHook());
+            _replSet->kill(_replSet->getPrimary());
+        }
+
+        void tearDown() {
+            ReplicaSetMonitor::remove(_replSet->getSetName(), true);
+            _replSet.reset();
+
+            // TODO: remove this after we remove replSetGetStatus from ReplicaSetMonitor.
+            mongo::ScopedDbConnection::clearPool();
+        }
+
+        MockReplicaSet* getReplSet() {
+            return _replSet.get();
+        }
+
+    private:
+        boost::scoped_ptr<MockReplicaSet> _replSet;
+    };
+
+    TEST_F(PrimaryDown, ReadFromPrimary) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_PrimaryOnly, BSONArray());
+        ASSERT_THROWS(replConn.query(IdentityNS, query), AssertionException);
+    }
+
+    TEST_F(PrimaryDown, SecondaryOnly) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_SecondaryOnly, BSONArray());
+
+        // Note: IdentityNS contains the name of the server.
+        auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
+        BSONObj doc = cursor->next();
+        ASSERT_EQUALS(replSet->getSecondaries().front(), doc[HostField.name()].str());
+    }
+
+    TEST_F(PrimaryDown, PrimaryPreferred) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_PrimaryPreferred, BSONArray());
+
+        // Note: IdentityNS contains the name of the server.
+        auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
+        BSONObj doc = cursor->next();
+        ASSERT_EQUALS(replSet->getSecondaries().front(), doc[HostField.name()].str());
+    }
+
+    TEST_F(PrimaryDown, SecondaryPreferred) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_SecondaryPreferred, BSONArray());
+
+        // Note: IdentityNS contains the name of the server.
+        auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
+        BSONObj doc = cursor->next();
+        ASSERT_EQUALS(replSet->getSecondaries().front(), doc[HostField.name()].str());
+    }
+
+    TEST_F(PrimaryDown, Nearest) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_Nearest, BSONArray());
+        auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
+        BSONObj doc = cursor->next();
+        ASSERT_EQUALS(replSet->getSecondaries().front(), doc[HostField.name()].str());
+    }
+
+    /**
+     * Setup for 2 member replica set with the secondary down.
+     */
+    class SecondaryDown: public mongo::unittest::Test {
+    protected:
+        void setUp() {
+            _replSet.reset(new MockReplicaSet("test", 2));
+            ConnectionString::setConnectionHook(
+                    mongo::MockConnRegistry::get()->getConnStrHook());
+
+            _replSet->kill(_replSet->getSecondaries().front());
+        }
+
+        void tearDown() {
+            ReplicaSetMonitor::remove(_replSet->getSetName(), true);
+            _replSet.reset();
+
+            // TODO: remove this after we remove replSetGetStatus from ReplicaSetMonitor.
+            mongo::ScopedDbConnection::clearPool();
+        }
+
+        MockReplicaSet* getReplSet() {
+            return _replSet.get();
+        }
+
+    private:
+        boost::scoped_ptr<MockReplicaSet> _replSet;
+    };
+
+    TEST_F(SecondaryDown, ReadFromPrimary) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_PrimaryOnly, BSONArray());
+
+        // Note: IdentityNS contains the name of the server.
+        auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
+        BSONObj doc = cursor->next();
+        ASSERT_EQUALS(replSet->getPrimary(), doc[HostField.name()].str());
+    }
+
+    TEST_F(SecondaryDown, SecondaryOnly) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_SecondaryOnly, BSONArray());
+        ASSERT_THROWS(replConn.query(IdentityNS, query), AssertionException);
+    }
+
+    TEST_F(SecondaryDown, PrimaryPreferred) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_PrimaryPreferred, BSONArray());
+
+        // Note: IdentityNS contains the name of the server.
+        auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
+        BSONObj doc = cursor->next();
+        ASSERT_EQUALS(replSet->getPrimary(), doc[HostField.name()].str());
+    }
+
+    TEST_F(SecondaryDown, SecondaryPreferred) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_SecondaryPreferred, BSONArray());
+
+        // Note: IdentityNS contains the name of the server.
+        auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
+        BSONObj doc = cursor->next();
+        ASSERT_EQUALS(replSet->getPrimary(), doc[HostField.name()].str());
+    }
+
+    TEST_F(SecondaryDown, Nearest) {
+        MockReplicaSet* replSet = getReplSet();
+        DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+
+        Query query;
+        query.readPref(mongo::ReadPreference_Nearest, BSONArray());
+
+        // Note: IdentityNS contains the name of the server.
+        auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
+        BSONObj doc = cursor->next();
+        ASSERT_EQUALS(replSet->getPrimary(), doc[HostField.name()].str());
+    }
+
     /**
      * Warning: Tests running this fixture cannot be run in parallel with other tests
      * that uses ConnectionString::setConnectionHook
      */
     class TaggedFiveMemberRS: public mongo::unittest::Test {
     protected:
-        static const string IdentityNS;
-        static const BSONField<string> HostField;
-
         void setUp() {
             _replSet.reset(new MockReplicaSet("test", 5));
             _originalConnectionHook = ConnectionString::getConnectionHook();
@@ -153,6 +489,8 @@ namespace mongo_test {
             ConnectionString::setConnectionHook(_originalConnectionHook);
             ReplicaSetMonitor::remove(_replSet->getSetName(), true);
             _replSet.reset();
+
+            // TODO: remove this after we remove replSetGetStatus from ReplicaSetMonitor.
             mongo::ScopedDbConnection::clearPool();
         }
 
@@ -165,9 +503,6 @@ namespace mongo_test {
         boost::scoped_ptr<MockReplicaSet> _replSet;
     };
 
-    const string TaggedFiveMemberRS::IdentityNS("local.me");
-    const BSONField<string> TaggedFiveMemberRS::HostField("host", "bad");
-
     TEST_F(TaggedFiveMemberRS, ConnShouldPinIfSameSettings) {
         MockReplicaSet* replSet = getReplSet();
         vector<HostAndPort> seedList;
@@ -179,6 +514,8 @@ namespace mongo_test {
         {
             Query query;
             query.readPref(mongo::ReadPreference_PrimaryPreferred, BSONArray());
+
+            // Note: IdentityNS contains the name of the server.
             auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
             BSONObj doc = cursor->next();
             dest = doc[HostField.name()].str();
@@ -205,6 +542,8 @@ namespace mongo_test {
         {
             Query query;
             query.readPref(mongo::ReadPreference_SecondaryPreferred, BSONArray());
+
+            // Note: IdentityNS contains the name of the server.
             auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
             BSONObj doc = cursor->next();
             dest = doc[HostField.name()].str();
@@ -233,6 +572,8 @@ namespace mongo_test {
             Query query;
             query.readPref(mongo::ReadPreference_SecondaryPreferred,
                     BSON_ARRAY(BSON("dc" << "sf")));
+
+            // Note: IdentityNS contains the name of the server.
             auto_ptr<DBClientCursor> cursor = replConn.query(IdentityNS, query);
             BSONObj doc = cursor->next();
             dest = doc[HostField.name()].str();
@@ -261,6 +602,8 @@ namespace mongo_test {
 
         string dest;
         mongo::DBClientConnection& secConn = replConn.slaveConn();
+
+        // Note: IdentityNS contains the name of the server.
         auto_ptr<DBClientCursor> cursor = secConn.query(IdentityNS, Query());
         BSONObj doc = cursor->next();
         dest = doc[HostField.name()].str();
diff --git a/src/mongo/dbtests/mock/mock_remote_db_server.cpp b/src/mongo/dbtests/mock/mock_remote_db_server.cpp
index e78d245c70c..9d8506b37ba 100644
--- a/src/mongo/dbtests/mock/mock_remote_db_server.cpp
+++ b/src/mongo/dbtests/mock/mock_remote_db_server.cpp
@@ -24,6 +24,7 @@ using std::string;
 using std::vector;
 
 namespace mongo {
+
     MockRemoteDBServer::CircularBSONIterator::CircularBSONIterator(
             const vector<BSONObj>& replyVector) {
         for (std::vector<mongo::BSONObj>::const_iterator iter = replyVector.begin();
@@ -54,6 +55,7 @@ namespace mongo {
             _cmdCount(0),
             _queryCount(0),
             _instanceID(0) {
+        insert(IdentityNS, BSON(HostField(hostAndPort)), 0);
     }
 
     MockRemoteDBServer::~MockRemoteDBServer() {
diff --git a/src/mongo/dbtests/mock/mock_remote_db_server.h b/src/mongo/dbtests/mock/mock_remote_db_server.h
index 6aaba91113c..0455e755d07 100644
--- a/src/mongo/dbtests/mock/mock_remote_db_server.h
+++ b/src/mongo/dbtests/mock/mock_remote_db_server.h
@@ -19,12 +19,17 @@
 #include <string>
 #include <vector>
 
+#include "mongo/bson/bson_field.h"
 #include "mongo/bson/bsonobjbuilder.h"
 #include "mongo/client/dbclientinterface.h"
 #include "mongo/platform/unordered_map.h"
 #include "mongo/util/concurrency/spin_lock.h"
 
 namespace mongo {
+
+    const std::string IdentityNS("local.me");
+    const BSONField<string> HostField("host");
+
     /**
      * A very simple mock that acts like a database server. Every object keeps track of its own
      * InstanceID, which initially starts at zero and increments every time it is restarted.
@@ -51,6 +56,9 @@ namespace mongo {
          * 1. hostAndPort of this server should start with $.
          * 2. No other instance has the same hostAndPort as this.
          *
+         * This server will also contain the hostAndPort inside the IdentityNS
+         * collection. This is convenient for testing query routing.
+         *
          * @param hostAndPort the host name with port for this server.
          *
          * @see MockConnRegistry
@@ -70,7 +78,7 @@ namespace mongo {
         /**
          * Shuts down this server. Any operations on this server with an InstanceID
          * less than or equal to the current one will throw a mongo::SocketException.
-         * To bring the server up again, use the #reboot method.
+         * To bring the server up again, use the reboot method.
          */
         void shutdown();