ut:add e2e test for external launcher (#2091)

### What this PR does / why we need it?
This pr add e2e testcase to make sure initialize LLM by
external_launcher method is ok.

### Does this PR introduce _any_ user-facing change?
not involved
### How was this patch tested?
not involved

- vLLM version: v0.10.0
- vLLM main:
2836dd73f1

Signed-off-by: Ronald1995 <ronaldautomobile@163.com>

tests/e2e/multicard/test_external_launcher.py

@@ -0,0 +1,73 @@
+#
+# Copyright (c) 2025 Huawei Technologies Co., Ltd. All Rights Reserved.
+# Copyright 2023 The vLLM team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+"""
+Compare the outputs of vLLM with and without aclgraph.
+
+Run `pytest tests/multicard/test_external_launcher.py`.
+"""
+
+import os
+import subprocess
+import sys
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+
+MODELS = ["Qwen/Qwen3-0.6B"]
+
+
+@pytest.mark.parametrize("model", MODELS)
+@patch.dict(os.environ, {"ASCEND_RT_VISIBLE_DEVICES": "0,1,2,3"})
+def test_external_launcher(model):
+    script = Path(
+        __file__
+    ).parent.parent.parent.parent / "examples" / "offline_external_launcher.py"
+    env = os.environ.copy()
+    # TODO: Change to 2 when ci machine has 4 cards
+    cmd = [
+        sys.executable,
+        str(script),
+        "--model",
+        model,
+        "--tp-size",
+        "1",
+        "--node-size",
+        "1",
+        "--node-rank",
+        "0",
+        "--proc-per-node",
+        "2",
+        "--trust-remote-code",
+    ]
+
+    print(f"Running subprocess: {' '.join(cmd)}")
+    proc = subprocess.run(
+        cmd,
+        env=env,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+        timeout=600,
+    )
+    output = proc.stdout.decode()
+
+    print(output)
+
+    assert "TP RANKS: [0]" in output
+    assert "TP RANKS: [1]" in output
+    assert "Generated text:" in output
+    assert proc.returncode == 0