[UT] Add new ut case for aclgraph in auto enable (#4031)

### What this PR does / why we need it?
add new ut case for aclgraph in auto enable

### Does this PR introduce _any_ user-facing change?
no

### How was this patch tested?
ut

- vLLM version: v0.11.0
- vLLM main:
83f478bb19

Signed-off-by: lilinsiman <lilinsiman@gmail.com>

tests/ut/test_platform.py

@@ -4,6 +4,7 @@ from unittest.mock import MagicMock, patch
 import pytest
 import torch
 from vllm.config.compilation import CUDAGraphMode
+from vllm.engine.arg_utils import EngineArgs
 from vllm.platforms import PlatformEnum
 
 from tests.ut.base import TestBase
@@ -722,3 +723,32 @@ class TestNPUPlatform(TestBase):
             self.platform.get_static_graph_wrapper_cls(),
             "vllm_ascend.compilation.acl_graph.ACLGraphWrapper",
         )
+
+    def test_aclgraph_enable(self):
+        config = EngineArgs()
+        VllmConfig = config.create_engine_config()
+        self.assertEqual(VllmConfig.compilation_config.cudagraph_mode,
+                         CUDAGraphMode.PIECEWISE)
+
+        with self.assertLogs(logger="vllm", level="INFO") as cm:
+            from vllm_ascend import platform
+
+            importlib.reload(platform)
+            self.platform.check_and_update_config(VllmConfig)
+            self.assertTrue(
+                "PIECEWISE compilation enabled on NPU. use_inductor not supported - "
+                "using only ACL Graph mode" in cm.output[1])
+            if vllm_version_is("0.11.0"):
+                self.assertEqual(
+                    VllmConfig.compilation_config.level,
+                    CompilationLevel.PIECEWISE,
+                )
+            else:
+                self.assertEqual(
+                    VllmConfig.compilation_config.mode,
+                    CompilationMode.VLLM_COMPILE,
+                )
+            self.assertEqual(
+                VllmConfig.compilation_config.cudagraph_mode,
+                CUDAGraphMode.PIECEWISE,
+            )