Do testing on isolated DB

tests/conftest.py

@@ -1,7 +1,26 @@
 """Pytest configuration and shared fixtures."""
 
+import os
+import shutil
+import tempfile
+from pathlib import Path
+
 import pytest
 
+# Use an isolated file-backed SQLite DB for tests that import app.main/TestClient.
+# This must be set before app.config/app.database are imported, otherwise the global
+# Database instance will bind to the default runtime DB (data/meshcore.db).
+_TEST_DB_DIR = Path(tempfile.mkdtemp(prefix="meshcore-pytest-"))
+_TEST_DB_PATH = _TEST_DB_DIR / "meshcore.db"
+os.environ.setdefault("MESHCORE_DATABASE_PATH", str(_TEST_DB_PATH))
+
+
+@pytest.fixture(scope="session", autouse=True)
+def cleanup_test_db_dir():
+    """Clean up temporary pytest DB directory after the test session."""
+    yield
+    shutil.rmtree(_TEST_DB_DIR, ignore_errors=True)
+
 
 @pytest.fixture
 def sample_channel_key():