diff --git a/quic/test_tools/quic_test_utils.cc b/quic/test_tools/quic_test_utils.cc
index aca0a57..d74df6a 100644
--- a/quic/test_tools/quic_test_utils.cc
+++ b/quic/test_tools/quic_test_utils.cc
@@ -47,6 +47,18 @@
                           sizeof(connection_id64_net));
 }
 
+QuicConnectionId TestConnectionIdNineBytesLong(uint64_t connection_number) {
+  const uint64_t connection_number_net =
+      QuicEndian::HostToNet64(connection_number);
+  char connection_id_bytes[9] = {};
+  static_assert(
+      sizeof(connection_id_bytes) == 1 + sizeof(connection_number_net),
+      "bad lengths");
+  memcpy(connection_id_bytes + 1, &connection_number_net,
+         sizeof(connection_number_net));
+  return QuicConnectionId(connection_id_bytes, sizeof(connection_id_bytes));
+}
+
 uint64_t TestConnectionIdToUInt64(QuicConnectionId connection_id) {
   DCHECK_EQ(connection_id.length(), kQuicDefaultConnectionIdLength);
   uint64_t connection_id64_net = 0;
diff --git a/quic/test_tools/quic_test_utils.h b/quic/test_tools/quic_test_utils.h
index 715fbf3..5c70c64 100644
--- a/quic/test_tools/quic_test_utils.h
+++ b/quic/test_tools/quic_test_utils.h
@@ -42,6 +42,10 @@
 // given number, such as an index.
 QuicConnectionId TestConnectionId(uint64_t connection_number);
 
+// A generic predictable connection ID suited for testing, generated from a
+// given number, such as an index. Guaranteed to be 9 bytes long.
+QuicConnectionId TestConnectionIdNineBytesLong(uint64_t connection_number);
+
 // Extracts the connection number passed to TestConnectionId().
 uint64_t TestConnectionIdToUInt64(QuicConnectionId connection_id);