[UT] Add ut for none hash (#17892)

Signed-off-by: Andy Xie <andy.xning@gmail.com>

tests/v1/core/test_kv_cache_utils.py

 # SPDX-License-Identifier: Apache-2.0
+import importlib
 
 import pytest
 import torch
@@ -10,8 +11,7 @@ from vllm.utils import GiB_bytes, sha256
 from vllm.v1.core.kv_cache_manager import KVCacheManager
 # disable yapf here as it formats differently than isort such that both fail
 # yapf: disable
-from vllm.v1.core.kv_cache_utils import (NONE_HASH, BlockHashType,
-                                         FreeKVCacheBlockQueue, KVCacheBlock,
+from vllm.v1.core.kv_cache_utils import (FreeKVCacheBlockQueue, KVCacheBlock,
                                          PrefixCachingMetrics,
                                          estimate_max_model_len,
                                          generate_block_hash_extra_keys,
@@ -65,13 +65,29 @@ def new_kv_cache_spec(block_size=16,
                              sliding_window=sliding_window)
 
 
-def test_none_hash():
-    assert NONE_HASH is not None
-    assert isinstance(NONE_HASH, int)
-    assert NONE_HASH != 0
+def test_none_hash(monkeypatch):
+    import vllm.v1.core.kv_cache_utils
+
+    # case 1: PYTHONHASHSEED is not set, use random
+    with monkeypatch.context() as m:
+        m.delenv('PYTHONHASHSEED', raising=False)
+        reloaded_kv_cache_utils = importlib.reload(vllm.v1.core.kv_cache_utils)
+        assert reloaded_kv_cache_utils.NONE_HASH is not None
+        assert isinstance(reloaded_kv_cache_utils.NONE_HASH, int)
+        assert reloaded_kv_cache_utils.NONE_HASH != 0
+
+    # case 2: PYTHONHASHSEED is set, use the seed
+    with monkeypatch.context() as m:
+        m.setenv('PYTHONHASHSEED', 'python hash seed')
+        reloaded_kv_cache_utils = importlib.reload(vllm.v1.core.kv_cache_utils)
+        assert reloaded_kv_cache_utils.NONE_HASH is not None
+        assert isinstance(reloaded_kv_cache_utils.NONE_HASH, int)
+        assert sha256('python hash seed') == reloaded_kv_cache_utils.NONE_HASH
 
 
 def test_kv_cache_block():
+    import vllm.v1.core.kv_cache_utils
+
     # Test KVCacheBlock initialization
     block = KVCacheBlock(block_id=0)
     assert block.block_id == 0
@@ -85,7 +101,8 @@ def test_kv_cache_block():
     assert block.ref_cnt == 0
 
     # Test block hash setting and resetting
-    block_hash = BlockHashType(hash_value=123, token_ids=(1, 2, 3))
+    block_hash = vllm.v1.core.kv_cache_utils.BlockHashType(hash_value=123,
+                                                           token_ids=(1, 2, 3))
     block.block_hash = block_hash
     assert block.block_hash == block_hash
 
@@ -259,13 +276,14 @@ def test_generate_block_hash_extra_keys_cache_salt():
 
 @pytest.mark.parametrize("hash_fn", [sha256, hash])
 def test_hash_block_tokens(hash_fn):
+    import vllm.v1.core.kv_cache_utils
     parent_block_hash = 123
     curr_block_token_ids = (1, 2, 3)
     extra_keys = ("key1", "key2")
 
     block_hash = hash_block_tokens(hash_fn, parent_block_hash,
                                    curr_block_token_ids, extra_keys)
-    assert isinstance(block_hash, BlockHashType)
+    assert isinstance(block_hash, vllm.v1.core.kv_cache_utils.BlockHashType)
     assert block_hash.hash_value == hash_fn(
         (parent_block_hash, curr_block_token_ids, extra_keys))
     assert block_hash.token_ids == curr_block_token_ids
@@ -274,6 +292,7 @@ def test_hash_block_tokens(hash_fn):
 
 @pytest.mark.parametrize("hash_fn", [sha256, hash])
 def test_hash_request_tokens(hash_fn):
+    import vllm.v1.core.kv_cache_utils
     request = make_request(
         request_id=0,
         prompt_token_ids=[_ for _ in range(6)],
@@ -288,8 +307,10 @@ def test_hash_request_tokens(hash_fn):
     block_hashes = hash_request_tokens(hash_fn, block_size, request)
 
     assert len(block_hashes) == 2
-    assert isinstance(block_hashes[0], BlockHashType)
-    assert isinstance(block_hashes[1], BlockHashType)
+    assert isinstance(block_hashes[0],
+                      vllm.v1.core.kv_cache_utils.BlockHashType)
+    assert isinstance(block_hashes[1],
+                      vllm.v1.core.kv_cache_utils.BlockHashType)
 
     # Check the first block
     assert block_hashes[0].token_ids == (0, 1, 2)