test: isolate embedding device env override tests

Agent-Logs-Url: https://github.com/MemPalace/mempalace/sessions/3213a67a-6871-4bb2-9ae0-23fa11001a22

Co-authored-by: igorls <4753812+igorls@users.noreply.github.com>

tests/test_config.py

@@ -20,12 +20,14 @@ def test_config_from_file():
     assert cfg.palace_path == "/custom/palace"
 
 
-def test_embedding_device_defaults_to_auto():
+def test_embedding_device_defaults_to_auto(monkeypatch):
+    monkeypatch.delenv("MEMPALACE_EMBEDDING_DEVICE", raising=False)
     cfg = MempalaceConfig(config_dir=tempfile.mkdtemp())
     assert cfg.embedding_device == "auto"
 
 
-def test_embedding_device_from_config_is_normalized(tmp_path):
+def test_embedding_device_from_config_is_normalized(tmp_path, monkeypatch):
+    monkeypatch.delenv("MEMPALACE_EMBEDDING_DEVICE", raising=False)
     with open(tmp_path / "config.json", "w") as f:
         json.dump({"embedding_device": "  CUDA  "}, f)
 
@@ -33,15 +35,13 @@ def test_embedding_device_from_config_is_normalized(tmp_path):
     assert cfg.embedding_device == "cuda"
 
 
-def test_embedding_device_env_overrides_config(tmp_path):
+def test_embedding_device_env_overrides_config(tmp_path, monkeypatch):
     with open(tmp_path / "config.json", "w") as f:
         json.dump({"embedding_device": "cpu"}, f)
-    os.environ["MEMPALACE_EMBEDDING_DEVICE"] = "  CoreML  "
-    try:
-        cfg = MempalaceConfig(config_dir=str(tmp_path))
-        assert cfg.embedding_device == "coreml"
-    finally:
-        del os.environ["MEMPALACE_EMBEDDING_DEVICE"]
+    monkeypatch.setenv("MEMPALACE_EMBEDDING_DEVICE", "  CoreML  ")
+
+    cfg = MempalaceConfig(config_dir=str(tmp_path))
+    assert cfg.embedding_device == "coreml"
 
 
 def test_env_override():