diff --git a/quic/test_tools/quic_test_client.cc b/quic/test_tools/quic_test_client.cc
index e2e33c7..ef92cb0 100644
--- a/quic/test_tools/quic_test_client.cc
+++ b/quic/test_tools/quic_test_client.cc
@@ -233,9 +233,14 @@
 }
 
 QuicConnectionId MockableQuicClient::GenerateNewConnectionId() {
-  return server_connection_id_overridden_
-             ? override_server_connection_id_
-             : QuicClient::GenerateNewConnectionId();
+  if (server_connection_id_overridden_) {
+    return override_server_connection_id_;
+  }
+  if (override_server_connection_id_length_ >= 0) {
+    return QuicUtils::CreateRandomConnectionId(
+        override_server_connection_id_length_);
+  }
+  return QuicClient::GenerateNewConnectionId();
 }
 
 void MockableQuicClient::UseConnectionId(
@@ -244,9 +249,20 @@
   override_server_connection_id_ = server_connection_id;
 }
 
+void MockableQuicClient::UseConnectionIdLength(
+    int server_connection_id_length) {
+  override_server_connection_id_length_ = server_connection_id_length;
+}
+
 QuicConnectionId MockableQuicClient::GetClientConnectionId() {
-  return client_connection_id_overridden_ ? override_client_connection_id_
-                                          : QuicClient::GetClientConnectionId();
+  if (client_connection_id_overridden_) {
+    return override_client_connection_id_;
+  }
+  if (override_client_connection_id_length_ >= 0) {
+    return QuicUtils::CreateRandomConnectionId(
+        override_client_connection_id_length_);
+  }
+  return QuicClient::GetClientConnectionId();
 }
 
 void MockableQuicClient::UseClientConnectionId(
@@ -255,6 +271,11 @@
   override_client_connection_id_ = client_connection_id;
 }
 
+void MockableQuicClient::UseClientConnectionIdLength(
+    int client_connection_id_length) {
+  override_client_connection_id_length_ = client_connection_id_length;
+}
+
 void MockableQuicClient::UseWriter(QuicPacketWriterWrapper* writer) {
   mockable_network_helper()->UseWriter(writer);
 }
@@ -769,12 +790,23 @@
   client_->UseConnectionId(server_connection_id);
 }
 
+void QuicTestClient::UseConnectionIdLength(int server_connection_id_length) {
+  DCHECK(!connected());
+  client_->UseConnectionIdLength(server_connection_id_length);
+}
+
 void QuicTestClient::UseClientConnectionId(
     QuicConnectionId client_connection_id) {
   DCHECK(!connected());
   client_->UseClientConnectionId(client_connection_id);
 }
 
+void QuicTestClient::UseClientConnectionIdLength(
+    int client_connection_id_length) {
+  DCHECK(!connected());
+  client_->UseClientConnectionIdLength(client_connection_id_length);
+}
+
 bool QuicTestClient::MigrateSocket(const QuicIpAddress& new_host) {
   return client_->MigrateSocket(new_host);
 }