Read replica usage in tests - tweaks (#16029)

* Refactor DB replica connection test_options

* Setup test databases explicitly

* Refactor FakeDbReplicaConnection and wrapp cursor creation with allow_writer

* Add comment to conftest.py

conftest.py

@@ -10,8 +10,15 @@
 
 from saleor.tests.utils import prepare_test_db_connections
 
-django.test.TransactionTestCase.databases = "__all__"
-django.test.TestCase.databases = "__all__"
+TEST_DATABASES = {
+    settings.DATABASE_CONNECTION_DEFAULT_NAME,
+    settings.DATABASE_CONNECTION_REPLICA_NAME,
+}
+# Here, we trick Django test cases into using multiple databases.
+# Thanks to this, we do not have to mark all tests
+# with @pytest.mark.django_db(databases=['default', 'replica'])
+django.test.TransactionTestCase.databases = TEST_DATABASES
+django.test.TestCase.databases = TEST_DATABASES
 
 prepare_test_db_connections()
 

saleor/settings.py

@@ -111,11 +111,9 @@ def get_url_from_env(name, *, schemes=None) -> Optional[str]:
         # and we need to update docs.
         # default="postgres://saleor_read_only:saleor@localhost:5432/saleor",
         conn_max_age=DB_CONN_MAX_AGE,
+        test_options={"MIRROR": DATABASE_CONNECTION_DEFAULT_NAME},
     ),
 }
-DATABASES[DATABASE_CONNECTION_REPLICA_NAME]["TEST"] = {
-    "MIRROR": DATABASE_CONNECTION_DEFAULT_NAME
-}
 
 DATABASE_ROUTERS = ["saleor.core.db_routers.PrimaryReplicaRouter"]
 

saleor/tests/utils.py

@@ -5,32 +5,35 @@
 from django.conf import settings
 from django.db import connections, transaction
 
+from ..core.db.connection import allow_writer
 
-class TestDBConnectionWrapper:
-    def __init__(self, conn, default_conn):
-        self._wrapped_conn = conn
-        self._default_conn = default_conn
+
+class FakeDbReplicaConnection:
+    def __init__(self, replica_conn):
+        self.replica_conn = replica_conn
+        self.writer_conn = connections[settings.DATABASE_CONNECTION_DEFAULT_NAME]
 
     def cursor(self, *args, **kwargs):
-        cursor = self._default_conn.cursor(*args, **kwargs)
-        cursor.db = self
+        with allow_writer():
+            cursor = self.writer_conn.cursor(*args, **kwargs)
+            cursor.db = self
         return cursor
 
     def chunked_cursor(self, *args, **kwargs):
-        cursor = self._default_conn.chunked_cursor(*args, **kwargs)
-        cursor.db = self
+        with allow_writer():
+            cursor = self.writer_conn.chunked_cursor(*args, **kwargs)
+            cursor.db = self
         return cursor
 
     def __getattr__(self, attr):
-        if attr in ["alias", "settings_dict"]:
-            return getattr(self._wrapped_conn, attr)
-        return getattr(self._default_conn, attr)
+        if attr == "alias":
+            return getattr(self.replica_conn, attr)
+        return getattr(self.writer_conn, attr)
 
 
 def prepare_test_db_connections():
     replica = settings.DATABASE_CONNECTION_REPLICA_NAME
-    default_conn = connections[settings.DATABASE_CONNECTION_DEFAULT_NAME]
-    connections[replica] = TestDBConnectionWrapper(connections[replica], default_conn)  # type: ignore
+    connections[replica] = FakeDbReplicaConnection(connections[replica])  # type: ignore
 
 
 def flush_post_commit_hooks():