diff --git a/tests/base.py b/tests/base.py
index c799bc2ad6..ed4892a092 100644
--- a/tests/base.py
+++ b/tests/base.py
@@ -62,6 +62,7 @@ class ApiTestCase(unittest.TestCase):
     """
     Set of helpers to make test development easier.
     """
+
     @classmethod
     def setUpClass(cls):
         pass
@@ -82,6 +83,7 @@ def setUp(self):
         app.app_context().push()
 
         from zou.app.utils import cache
+
         cache.clear()
 
     def tearDown(self):
@@ -233,11 +235,11 @@ def download_file(self, path, target_file_path, code=200):
         return open(target_file_path, "rb").read()
 
 
-
 class ApiDBTestCase(ApiTestCase):
     """
     Set of helpers for Api tests.
     """
+
     @classmethod
     def setUpClass(cls):
         """
@@ -246,6 +248,7 @@ def setUpClass(cls):
         """
         super(ApiDBTestCase, cls).setUpClass()
         from zou.app.utils import dbhelpers
+
         with app.app_context():
             dbhelpers.drop_all()
             dbhelpers.create_all()
@@ -258,10 +261,11 @@ def tearDownClass(cls):
         """
         super(ApiDBTestCase, cls).tearDownClass()
         from zou.app.utils import dbhelpers
+
         with app.app_context():
             dbhelpers.drop_all()
-    
-    def setUp(self):
+
+    def setUp(self, expire_on_commit=True):
         """
         Configure application before each test.
         set up database transaction.
@@ -270,9 +274,15 @@ def setUp(self):
 
         self._db_connection = db.engine.connect()
         self._db_transaction = self._db_connection.begin()
-        factory = sessionmaker(bind=self._db_connection, binds={})
-        self._db_session = scoped_session(factory, current_app._get_current_object)
-        db.session = self._db_session 
+        factory = sessionmaker(
+            bind=self._db_connection,
+            binds={},
+            expire_on_commit=expire_on_commit,
+        )
+        self._db_session = scoped_session(
+            factory, current_app._get_current_object
+        )
+        db.session = self._db_session
 
         self.generate_fixture_user()
         self.log_in_admin()
diff --git a/tests/chats/test_chat_routes.py b/tests/chats/test_chat_routes.py
index 09edc62ff2..d66603d5bd 100644
--- a/tests/chats/test_chat_routes.py
+++ b/tests/chats/test_chat_routes.py
@@ -1,11 +1,15 @@
+import os
+
 from tests.base import ApiDBTestCase
 
 from zou.app.services import chats_service
+from zou.app.stores import file_store
+from zou.app.utils import thumbnail
 
 
 class EventsRoutesTestCase(ApiDBTestCase):
     def setUp(self):
-        super(EventsRoutesTestCase, self).setUp()
+        super(EventsRoutesTestCase, self).setUp(expire_on_commit=False)
 
         self.generate_fixture_project_status()
         self.generate_fixture_project()
@@ -63,7 +67,7 @@ def test_get_chat_message(self):
         )
         self.assertEqual(message["id"], chat_message["id"])
 
-    """ def test_post_chat_message_with_attachment(self):
+    def test_post_chat_message_with_attachment(self):
         self.post(f"/actions/user/chats/{self.asset.id}/join", {}, 200)
         file_path_fixture = self.get_fixture_file_path(
             os.path.join("thumbnails", "th01.png"),
@@ -81,7 +85,7 @@ def test_get_chat_message(self):
         size = thumbnail.get_dimensions(
             file_store.get_local_picture_path("thumbnails", attachment_id)
         )
-        self.assertEqual(size, (150, 150)) """
+        self.assertEqual(size, (150, 150))
 
     def test_delete_chat_message(self):
         chat_message = self.generate_fixture_chat_message()