Fix popen_launch_server wait for 20 minutes when child process exits (#4777)

python/sglang/test/test_utils.py

 """Common utilities for testing and benchmarking"""
 
 import argparse
-import asyncio
 import copy
 import logging
 import os
@@ -64,7 +63,6 @@ DEFAULT_MODEL_NAME_FOR_NIGHTLY_EVAL_QUANT_TP1 = "hugging-quants/Meta-Llama-3.1-8
 DEFAULT_SMALL_MODEL_NAME_FOR_TEST_QWEN = "Qwen/Qwen2.5-1.5B-Instruct"
 DEFAULT_SMALL_VLM_MODEL_NAME = "Qwen/Qwen2-VL-2B"
 
-
 DEFAULT_EAGLE_TARGET_MODEL_FOR_TEST = "meta-llama/Llama-2-7b-chat-hf"
 DEFAULT_EAGLE_DRAFT_MODEL_FOR_TEST = "lmsys/sglang-EAGLE-llama2-chat-7B"
 
@@ -435,6 +433,11 @@ def popen_launch_server(
                     return process
             except requests.RequestException:
                 pass
+
+            return_code = process.poll()
+            if return_code is not None:
+                raise Exception(f"Server unexpectedly exits ({return_code=}).")
+
             time.sleep(10)
 
     kill_process_tree(process.pid)
@@ -888,7 +891,6 @@ def run_mulit_request_test(
     enable_overlap=False,
     chunked_prefill_size=32,
 ):
-
     def workload_func(base_url, model):
         def run_one(_):
             prompt = """