diff --git a/example/tasks/config.py b/example/tasks/config.py
index 6f06094..311e5eb 100644
--- a/example/tasks/config.py
+++ b/example/tasks/config.py
@@ -1,6 +1,7 @@
 """Configuration for Celery app."""
 
 import os
+import sys
 
 import redis
 
@@ -47,4 +48,4 @@
     print("Redis connection is working.")
 except redis.ConnectionError as e:
     print(f"Failed to connect to Redis: {e}")
-    exit(1)
+    sys.exit(1)
diff --git a/src/retsu/celery.py b/src/retsu/celery.py
index 8a6e90b..1508f02 100644
--- a/src/retsu/celery.py
+++ b/src/retsu/celery.py
@@ -7,6 +7,7 @@
 import celery
 
 from celery import chain, chord
+from public import public
 
 from retsu.core import ParallelTask, SerialTask
 
@@ -63,12 +64,14 @@ def get_chain_tasks(  # type: ignore
         return chain_tasks
 
 
+@public
 class ParallelCeleryTask(CeleryTask, ParallelTask):
     """Parallel Task for Celery."""
 
     ...
 
 
+@public
 class SerialCeleryTask(CeleryTask, SerialTask):
     """Serial Task for Celery."""
 
diff --git a/tests/celery_tasks.py b/tests/celery_tasks.py
index 15a8a25..fb41d9a 100644
--- a/tests/celery_tasks.py
+++ b/tests/celery_tasks.py
@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import os
+import sys
 
 from datetime import datetime
 from time import sleep
@@ -52,7 +53,7 @@
     print("Redis connection is working.")
 except redis.ConnectionError as e:
     print(f"Failed to connect to Redis: {e}")
-    exit(1)
+    sys.exit(1)
 
 
 @app.task  # type: ignore
diff --git a/tests/test_task_celery_serial.py b/tests/test_task_celery_serial.py
index b211439..509602a 100644
--- a/tests/test_task_celery_serial.py
+++ b/tests/test_task_celery_serial.py
@@ -2,34 +2,40 @@
 
 from __future__ import annotations
 
-from datetime import datetime
-from time import sleep
-from typing import Any, Generator
+from typing import Generator
 
 import pytest
 
-from retsu import SerialTask, Task
+from retsu.celery import SerialCeleryTask
 
+from .celery_tasks import task_sum
 
-class MyResultTask(SerialTask):
+
+class MyResultTask(SerialCeleryTask):
     """Task for the test."""
 
-    def task(self, *args, task_id: str, **kwargs) -> Any:  # type: ignore
-        """Return the sum of the given 2 numbers."""
-        a = kwargs.pop("a", 0)
-        b = kwargs.pop("b", 0)
-        result = a + b
-        return result
+    def get_chord_tasks(self, *args, **kwargs) -> list[celery.Signature]:
+        """Define the list of tasks for celery chord."""
+        x = kwargs.get("x")
+        y = kwargs.get("y")
+        task_id = kwargs.get("task_id")
+        return (
+            [task_sum.s(x, y, task_id)],
+            None,
+        )
 
 
-class MyTimestampTask(SerialTask):
+class MyTimestampTask(SerialCeleryTask):
     """Task for the test."""
 
-    def task(self, *args, task_id: str, **kwargs) -> Any:  # type: ignore
-        """Sleep the given seconds, and return the current timestamp."""
-        sleep_time = kwargs.pop("sleep", 0)
-        sleep(sleep_time)
-        return datetime.now().timestamp()
+    def get_chord_tasks(self, *args, **kwargs) -> list[celery.Signature]:
+        """Define the list of tasks for celery chord."""
+        seconds = kwargs.get("seconds")
+        task_id = kwargs.get("task_id")
+        return (
+            [task_sum.s(x, y, task_id, task_id)],
+            None,
+        )
 
 
 @pytest.fixture