diff --git a/quic/test_tools/quic_framer_peer.cc b/quic/test_tools/quic_framer_peer.cc
index 94493c3..eea4fd6 100644
--- a/quic/test_tools/quic_framer_peer.cc
+++ b/quic/test_tools/quic_framer_peer.cc
@@ -29,6 +29,13 @@
 }
 
 // static
+void QuicFramerPeer::SetLastSerializedClientConnectionId(
+    QuicFramer* framer,
+    QuicConnectionId client_connection_id) {
+  framer->last_serialized_client_connection_id_ = client_connection_id;
+}
+
+// static
 void QuicFramerPeer::SetLargestPacketNumber(QuicFramer* framer,
                                             QuicPacketNumber packet_number) {
   framer->largest_packet_number_ = packet_number;
diff --git a/quic/test_tools/quic_framer_peer.h b/quic/test_tools/quic_framer_peer.h
index 7a09a92..8496718 100644
--- a/quic/test_tools/quic_framer_peer.h
+++ b/quic/test_tools/quic_framer_peer.h
@@ -25,6 +25,9 @@
   static void SetLastSerializedServerConnectionId(
       QuicFramer* framer,
       QuicConnectionId server_connection_id);
+  static void SetLastSerializedClientConnectionId(
+      QuicFramer* framer,
+      QuicConnectionId client_connection_id);
   static void SetLargestPacketNumber(QuicFramer* framer,
                                      QuicPacketNumber packet_number);
   static void SetPerspective(QuicFramer* framer, Perspective perspective);
diff --git a/quic/test_tools/quic_test_client.cc b/quic/test_tools/quic_test_client.cc
index d4608ed..3e577a3 100644
--- a/quic/test_tools/quic_test_client.cc
+++ b/quic/test_tools/quic_test_client.cc
@@ -210,7 +210,9 @@
           QuicWrapUnique(
               new RecordingProofVerifier(std::move(proof_verifier)))),
       override_server_connection_id_(EmptyQuicConnectionId()),
-      server_connection_id_overridden_(false) {}
+      server_connection_id_overridden_(false),
+      override_client_connection_id_(EmptyQuicConnectionId()),
+      client_connection_id_overridden_(false) {}
 
 MockableQuicClient::~MockableQuicClient() {
   if (connected()) {
@@ -242,6 +244,17 @@
   override_server_connection_id_ = server_connection_id;
 }
 
+QuicConnectionId MockableQuicClient::GetClientConnectionId() {
+  return client_connection_id_overridden_ ? override_client_connection_id_
+                                          : QuicClient::GetClientConnectionId();
+}
+
+void MockableQuicClient::UseClientConnectionId(
+    QuicConnectionId client_connection_id) {
+  client_connection_id_overridden_ = true;
+  override_client_connection_id_ = client_connection_id;
+}
+
 void MockableQuicClient::UseWriter(QuicPacketWriterWrapper* writer) {
   mockable_network_helper()->UseWriter(writer);
 }
@@ -756,6 +769,12 @@
   client_->UseConnectionId(server_connection_id);
 }
 
+void QuicTestClient::UseClientConnectionId(
+    QuicConnectionId client_connection_id) {
+  DCHECK(!connected());
+  client_->UseClientConnectionId(client_connection_id);
+}
+
 bool QuicTestClient::MigrateSocket(const QuicIpAddress& new_host) {
   return client_->MigrateSocket(new_host);
 }
diff --git a/quic/test_tools/quic_test_client.h b/quic/test_tools/quic_test_client.h
index a4ee0d5..5f1b6fa 100644
--- a/quic/test_tools/quic_test_client.h
+++ b/quic/test_tools/quic_test_client.h
@@ -56,6 +56,8 @@
 
   QuicConnectionId GenerateNewConnectionId() override;
   void UseConnectionId(QuicConnectionId server_connection_id);
+  QuicConnectionId GetClientConnectionId() override;
+  void UseClientConnectionId(QuicConnectionId client_connection_id);
 
   void UseWriter(QuicPacketWriterWrapper* writer);
   void set_peer_address(const QuicSocketAddress& address);
@@ -72,6 +74,9 @@
   // Server connection ID to use, if server_connection_id_overridden_
   QuicConnectionId override_server_connection_id_;
   bool server_connection_id_overridden_;
+  // Client connection ID to use, if client_connection_id_overridden_
+  QuicConnectionId override_client_connection_id_;
+  bool client_connection_id_overridden_;
   CachedNetworkParameters cached_network_paramaters_;
 };
 
@@ -222,6 +227,9 @@
   // Configures client_ to use a specific server connection ID instead of a
   // random one.
   void UseConnectionId(QuicConnectionId server_connection_id);
+  // Configures client_ to use a specific client connection ID instead of an
+  // empty one.
+  void UseClientConnectionId(QuicConnectionId client_connection_id);
 
   // Returns nullptr if the maximum number of streams have already been created.
   QuicSpdyClientStream* GetOrCreateStream();