diff --git a/tests/conftest.py b/tests/conftest.py
index 6a2132622..f7039d74d 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -14,6 +14,18 @@ if str(PROJECT_ROOT) not in sys.path:
     sys.path.insert(0, str(PROJECT_ROOT))
 
 
+@pytest.fixture(autouse=True)
+def _isolate_hermes_home(tmp_path, monkeypatch):
+    """Redirect HERMES_HOME to a temp dir so tests never write to ~/.hermes/."""
+    fake_home = tmp_path / "hermes_test"
+    fake_home.mkdir()
+    (fake_home / "sessions").mkdir()
+    (fake_home / "cron").mkdir()
+    (fake_home / "memories").mkdir()
+    (fake_home / "skills").mkdir()
+    monkeypatch.setenv("HERMES_HOME", str(fake_home))
+
+
 @pytest.fixture()
 def tmp_dir(tmp_path):
     """Provide a temporary directory that is cleaned up automatically."""
diff --git a/tests/tools/test_debug_helpers.py b/tests/tools/test_debug_helpers.py
index b1c528b6e..e2840e62a 100644
--- a/tests/tools/test_debug_helpers.py
+++ b/tests/tools/test_debug_helpers.py
@@ -26,9 +26,11 @@ class TestDebugSessionDisabled:
 
     def test_save_noop(self, tmp_path):
         ds = DebugSession("test_tool", env_var="FAKE_DEBUG_VAR_XYZ")
-        ds.log_dir = tmp_path
+        log_dir = tmp_path / "debug_logs"
+        log_dir.mkdir()
+        ds.log_dir = log_dir
         ds.save()
-        assert list(tmp_path.iterdir()) == []
+        assert list(log_dir.iterdir()) == []
 
     def test_get_session_info_disabled(self):
         ds = DebugSession("test_tool", env_var="FAKE_DEBUG_VAR_XYZ")