Initialize postgres_cluster fixture lazily

src/aiida/tools/pytest_fixtures/storage.py

@@ -4,39 +4,49 @@
 
 import pathlib
 import typing as t
+from uuid import uuid4
 
 import pytest
+from pgtest.pgtest import PGTest
 
 if t.TYPE_CHECKING:
     from pgtest.pgtest import PGTest
 
 
-@pytest.fixture(scope='session')
-def postgres_cluster():
-    """Create a temporary and isolated PostgreSQL cluster using ``pgtest`` and cleanup after the yield.
+class PostgresCluster:
+    def __init__(self):
+        # We initialize the cluster lazily
+        self.cluster = None
 
-    :param database_name: Name of the database.
-    :param database_username: Username to use for authentication.
-    :param database_password: Password to use for authentication.
-    :returns: Dictionary with parameters to connect to the PostgreSQL cluster.
-    """
-    from uuid import uuid4
+    def _create(self):
+        try:
+            self.cluster = PGTest()
+        except OSError as e:
+            raise RuntimeError('Could not initialize PostgreSQL cluster') from e
 
-    from pgtest.pgtest import PGTest
+    def _close(self):
+        if self.cluster is not None:
+            self.cluster.close()
 
     def create_database(
-        database_name: str | None = None, database_username: str | None = None, database_password: str | None = None
+        self,
+        database_name: str | None = None,
+        database_username: str | None = None,
+        database_password: str | None = None,
     ) -> dict[str, str]:
         from aiida.manage.external.postgres import Postgres
 
+        if self.cluster is None:
+            self._create()
+
         postgres_config = {
             'database_engine': 'postgresql_psycopg2',
             'database_name': database_name or str(uuid4()),
             'database_username': database_username or 'guest',
             'database_password': database_password or 'guest',
         }
 
-        postgres = Postgres(interactive=False, quiet=True, dbinfo=cluster.dsn)  # type: ignore[union-attr]
+        postgres = Postgres(interactive=False, quiet=True, dbinfo=self.cluster.dsn)  # type: ignore[union-attr]
         if not postgres.dbuser_exists(postgres_config['database_username']):
             postgres.create_dbuser(
                 postgres_config['database_username'], postgres_config['database_password'], 'CREATEDB'
@@ -48,16 +58,21 @@ def create_database(
 
         return postgres_config
 
-    cluster = None
-    try:
-        cluster = PGTest()
-        cluster.create_database = create_database
-        yield cluster
-    except OSError:
-        yield None
-    finally:
-        if cluster is not None:
-            cluster.close()
+
+# TODO: Update docstring accordingly
+@pytest.fixture(scope='session')
+def postgres_cluster():
+    """Create a temporary and isolated PostgreSQL cluster using ``pgtest`` and cleanup after the yield.
+
+    :param database_name: Name of the database.
+    :param database_username: Username to use for authentication.
+    :param database_password: Password to use for authentication.
+    :returns: Dictionary with parameters to connect to the PostgreSQL cluster.
+    """
+
+    cluster = PostgresCluster()
+    yield cluster
+    cluster._close()
 
 
 @pytest.fixture(scope='session')
@@ -78,10 +93,6 @@ def config_psql_dos(
     def factory(
         database_name: str | None = None, database_username: str | None = None, database_password: str | None = None
     ) -> dict[str, t.Any]:
-        if not postgres_cluster:
-            msg = 'Could not initialize PostgreSQL cluster'
-            raise RuntimeError(msg)
-
         storage_config: dict[str, t.Any] = postgres_cluster.create_database(
             database_name=database_name,
             database_username=database_username,