[PD] Add simple unit test for disaggregation feature (#5654)

Signed-off-by: Shangming Cai <caishangming@linux.alibaba.com>

python/sglang/test/test_utils.py

@@ -478,6 +478,81 @@ def popen_launch_server(
     raise TimeoutError("Server failed to start within the timeout period.")
 
 
+def popen_launch_pd_server(
+    model: str,
+    base_url: str,
+    timeout: float,
+    api_key: Optional[str] = None,
+    other_args: list[str] = (),
+    env: Optional[dict] = None,
+    return_stdout_stderr: Optional[tuple] = None,
+):
+    _, host, port = base_url.split(":")
+    host = host[2:]
+
+    command = "sglang.launch_server"
+
+    command = [
+        "python3",
+        "-m",
+        command,
+        "--model-path",
+        model,
+        *[str(x) for x in other_args],
+    ]
+
+    command.extend(
+        [
+            "--host",
+            host,
+            "--port",
+            port,
+        ]
+    )
+
+    if api_key:
+        command += ["--api-key", api_key]
+
+    print(f"command={' '.join(command)}")
+
+    if return_stdout_stderr:
+        process = subprocess.Popen(
+            command,
+            stdout=return_stdout_stderr[0],
+            stderr=return_stdout_stderr[1],
+            env=env,
+            text=True,
+        )
+    else:
+        process = subprocess.Popen(command, stdout=None, stderr=None, env=env)
+
+    start_time = time.time()
+    with requests.Session() as session:
+        while time.time() - start_time < timeout:
+            try:
+                headers = {
+                    "Content-Type": "application/json; charset=utf-8",
+                    "Authorization": f"Bearer {api_key}",
+                }
+                response = session.get(
+                    f"{base_url}/health",
+                    headers=headers,
+                )
+                if response.status_code == 200:
+                    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)
+    raise TimeoutError("Server failed to start within the timeout period.")
+
+
 def run_with_timeout(
     func: Callable,
     args: tuple = (),