Add schema migrations for index

src/tests/test_migrations.py

@@ -0,0 +1,34 @@
+import sys
+from pathlib import Path
+import pytest
+from cryptography.fernet import Fernet
+
+sys.path.append(str(Path(__file__).resolve().parents[1]))
+
+from password_manager.encryption import EncryptionManager
+from password_manager.vault import Vault
+from password_manager.migrations import LATEST_VERSION
+
+
+def setup(tmp_path: Path):
+    key = Fernet.generate_key()
+    enc_mgr = EncryptionManager(key, tmp_path)
+    vault = Vault(enc_mgr, tmp_path)
+    return enc_mgr, vault
+
+
+def test_migrate_v0_to_v1(tmp_path: Path):
+    enc_mgr, vault = setup(tmp_path)
+    legacy = {"passwords": {"0": {"website": "a", "length": 8}}}
+    enc_mgr.save_json_data(legacy)
+    data = vault.load_index()
+    assert data["schema_version"] == LATEST_VERSION
+    assert data["passwords"] == legacy["passwords"]
+
+
+def test_error_on_future_version(tmp_path: Path):
+    enc_mgr, vault = setup(tmp_path)
+    future = {"schema_version": LATEST_VERSION + 1, "passwords": {}}
+    enc_mgr.save_json_data(future)
+    with pytest.raises(ValueError):
+        vault.load_index()