[Test] Add ut test for torchair (#4287)

### What this PR does / why we need it?
The current community lacks unit tests (UT) for files such as
torchair_worker, mtp_proposer, and model_runner. Therefore, UT coverage
for these files needs to be added.

### Does this PR introduce _any_ user-facing change?
NO
### How was this patch tested?

- vLLM version: v0.11.0
- vLLM main:
2918c1b49c

---------

Signed-off-by: CodeNine-CJ <chenjian343@huawei.com>

tests/ut/torchair/test_torchair_worker.py

@@ -0,0 +1,107 @@
+from unittest.mock import MagicMock, patch
+
+import torch
+from vllm.config import CacheConfig, ModelConfig, ParallelConfig, VllmConfig
+
+from tests.ut.base import TestBase
+from vllm_ascend.utils import vllm_version_is
+
+init_cache_hf_modules_path = "vllm.utils.init_cached_hf_modules" if vllm_version_is(
+    "0.11.0") else "vllm.utils.import_utils.init_cached_hf_modules"
+
+
+class TestNPUTorchairWorker(TestBase):
+
+    def setUp(self):
+        self.cache_config_mock = MagicMock(spec=CacheConfig)
+        self.cache_config_mock.cache_type = "auto"
+
+        self.model_config_mock = MagicMock(spec=ModelConfig)
+        self.model_config_mock.dtype = torch.float16
+        self.model_config_mock.trust_remote_code = False
+
+        self.hf_config_mock = MagicMock()
+        self.hf_config_mock.model_type = "test_model"
+        if hasattr(self.hf_config_mock, 'index_topk'):
+            delattr(self.hf_config_mock, 'index_topk')
+
+        self.model_config_mock.hf_config = self.hf_config_mock
+
+        self.parallel_config_mock = MagicMock(spec=ParallelConfig)
+
+        self.vllm_config_mock = MagicMock(spec=VllmConfig)
+        self.vllm_config_mock.cache_config = self.cache_config_mock
+        self.vllm_config_mock.model_config = self.model_config_mock
+        self.vllm_config_mock.parallel_config = self.parallel_config_mock
+        self.vllm_config_mock.additional_config = None
+        self.vllm_config_mock.load_config = None
+        self.vllm_config_mock.scheduler_config = None
+        self.vllm_config_mock.device_config = None
+        self.vllm_config_mock.compilation_config = None
+
+        self.local_rank = 0
+        self.rank = 0
+        self.distributed_init_method = "tcp://localhost:12345"
+        self.is_driver_worker = False
+
+    @patch(
+        "vllm_ascend.worker.worker_v1.NPUWorker._init_worker_distributed_environment"
+    )
+    @patch("vllm_ascend.worker.worker_v1.NPUPlatform")
+    def test_init_device(self, mock_platform, mock_init_dist_env):
+        from vllm_ascend.worker.worker_v1 import NPUWorker
+
+        mock_platform.mem_get_info.return_value = (1000, 2000)
+
+        with patch.object(NPUWorker, "__init__", lambda x, **kwargs: None):
+            worker = NPUWorker()
+            worker.local_rank = 1
+            worker.model_config = MagicMock()
+            worker.model_config.seed = 42
+            worker.vllm_config = MagicMock()
+
+            result = worker._init_device()
+
+            mock_platform.set_device.assert_called_once()
+            call_args = mock_platform.set_device.call_args[0][0]
+            self.assertEqual(str(call_args), "npu:1")
+
+            mock_platform.empty_cache.assert_called_once()
+            mock_platform.seed_everything.assert_called_once_with(42)
+            mock_platform.mem_get_info.assert_called_once()
+            mock_init_dist_env.assert_called_once()
+
+            self.assertEqual(str(result), "npu:1")
+            self.assertEqual(worker.init_npu_memory, 1000)
+
+    @patch(
+        "vllm_ascend.worker.worker_v1.NPUWorker._init_worker_distributed_environment"
+    )
+    @patch("vllm_ascend.worker.worker_v1.NPUPlatform")
+    def test_init_device_torchair_worker(self, mock_platform,
+                                         mock_init_dist_env):
+        from vllm_ascend.torchair.torchair_worker import NPUTorchairWorker
+
+        mock_platform.mem_get_info.return_value = (1000, 2000)
+
+        with patch.object(NPUTorchairWorker, "__init__",
+                          lambda x, **kwargs: None):
+            worker = NPUTorchairWorker()
+            worker.local_rank = 1
+            worker.model_config = MagicMock()
+            worker.model_config.seed = 42
+            worker.vllm_config = MagicMock()
+
+            result = worker._init_device()
+
+            mock_platform.set_device.assert_called_once()
+            call_args = mock_platform.set_device.call_args[0][0]
+            self.assertEqual(str(call_args), "npu:1")
+
+            mock_platform.empty_cache.assert_called_once()
+            mock_platform.seed_everything.assert_called_once_with(42)
+            mock_platform.mem_get_info.assert_called_once()
+            mock_init_dist_env.assert_called_once()
+
+            self.assertEqual(str(result), "npu:1")
+            self.assertEqual(worker.init_npu_memory, 1000)