Add tests for generic relationship batch fetching

tests/batch_fetch/test_generic_relationship.py

@@ -0,0 +1,44 @@
+from __future__ import unicode_literals
+import sqlalchemy as sa
+from tests import TestCase
+from sqlalchemy_utils import batch_fetch, generic_relationship
+
+
+class TestBatchFetchGenericRelationship(TestCase):
+    def create_models(self):
+        class Building(self.Base):
+            __tablename__ = 'building'
+            id = sa.Column(sa.Integer, primary_key=True)
+
+        class User(self.Base):
+            __tablename__ = 'user'
+            id = sa.Column(sa.Integer, primary_key=True)
+
+        class Event(self.Base):
+            __tablename__ = 'event'
+            id = sa.Column(sa.Integer, primary_key=True)
+
+            object_type = sa.Column(sa.Unicode(255))
+            object_id = sa.Column(sa.Integer, nullable=False)
+
+            object = generic_relationship(object_type, object_id)
+
+        self.Building = Building
+        self.User = User
+        self.Event = Event
+
+    def test_batch_fetch(self):
+        user = self.User()
+
+        self.session.add(user)
+        self.session.commit()
+        event = self.Event(object=user)
+        self.session.add(event)
+        self.session.commit()
+
+        events = self.session.query(self.Event).all()
+        batch_fetch(events, 'object')
+        query_count = self.connection.query_count
+        events[0].object
+
+        assert self.connection.query_count == query_count