Add readiness wait for TiDB cluster before tests

Add wait_for_tidb function that waits for TiDB to be ready before
tests start. Uses extended timeout (240s) for 6.1.x and 6.5.x versions
which need longer startup time, matching the behavior in tidb-playground.sh.

This fixes test timeouts where tests were trying to connect before
TiDB was ready to accept connections.

Author: zph

scripts/tidb-test-cluster.sh

@@ -170,6 +170,39 @@ function run_tidb() {
 	fi
 }
 
+function wait_for_tidb() {
+	local _mysql_port=$1
+	local _version=$2
+	echo "==> Waiting for TiDB to be ready..."
+	
+	# Determine timeout based on TiDB version
+	# Versions 6.1.x and 6.5.x need longer startup time
+	if [[ "${_version}" == 6.1.* ]] || [[ "${_version}" == 6.5.* ]]; then
+		TIMEOUT=240  # 4 minutes for older versions
+		echo "Using extended timeout (240s) for TiDB ${_version}"
+	else
+		TIMEOUT=120  # 2 minutes for newer versions
+	fi
+	
+	# Wait for TiDB to be ready
+	for i in $(seq 1 ${TIMEOUT}); do
+		if mysql -h 127.0.0.1 -P ${_mysql_port} -u root -e 'SELECT 1' >/dev/null 2>&1; then
+			echo "TiDB is ready!"
+			return 0
+		fi
+		sleep 1
+		if [ $((i % 10)) -eq 0 ]; then
+			printf "."
+		fi
+	done
+	
+	echo ""
+	echo "ERROR: TiDB failed to start within ${TIMEOUT} seconds"
+	echo "Checking container logs..."
+	docker logs tidb 2>&1 | tail -20 || true
+	return 1
+}
+
 function main() {
 	  parse_params "$@"
 		if [[ "$SCRIPT_INIT" = "true" ]]; then
@@ -178,7 +211,8 @@ function main() {
 			${DOCKER} network create ${DOCKER_NETWORK} && \
 			run_pd && \
 			run_tikv && \
-			run_tidb $MYSQL_PORT
+			run_tidb $MYSQL_PORT && \
+			wait_for_tidb $MYSQL_PORT $MYSQL_VERSION
 
 		else
 			script_usage