Initialise db connection lazily, use isolated asyncio test case

lacre/dbkeyring.py

@@ -28,8 +28,13 @@ class DatabaseKeyRing(KeyRing):
 
     def __init__(self, database_url, schema: KeyRingSchema):
         self._schema = schema
-        self._engine = sqlalchemy.create_engine(database_url)
-        self._connection = self._engine.connect()
+        self._url = database_url
+        self._initialised = False
+
+    def _ensure_initialised(self):
+        if not self._initialised:
+            self._engine = sqlalchemy.create_engine(self._url)
+            self._connection = self._engine.connect()
 
     def load(self):
         """Do nothing, database contents doesn't need to be cached."""
@@ -37,6 +42,7 @@ class DatabaseKeyRing(KeyRing):
 
     async def freeze_identities(self) -> KeyCache:
         """Return a static, async-safe copy of the identity map."""
+        self._ensure_initialised()
         return self._load_identities()
 
     def _load_identities(self) -> KeyCache:

test/modules/test_dbkeyring.py

@@ -4,13 +4,13 @@ import lacre.dbkeyring as dbk
 
 import unittest
 
-class LacreDbKeyringTest(unittest.TestCase):
-    def test_load_keys(self):
+class LacreDbKeyringTest(unittest.IsolatedAsyncioTestCase):
+    async def test_load_keys(self):
         db_url = 'sqlite:///test/lacre.db'
         schema = dbk.KeyRingSchema()
         db = dbk.DatabaseKeyRing(db_url, schema)
 
-        identities = db.freeze_identities()
+        identities = await db.freeze_identities()
 
         self.assertTrue('1CD245308F0963D038E88357973CF4D9387C44D7' in identities)
         self.assertTrue(identities.has_email('alice@disposlab'))