diff --git a/src/line_notifier.py b/src/line_notifier.py
index e5e6437..217b46c 100644
--- a/src/line_notifier.py
+++ b/src/line_notifier.py
@@ -2,18 +2,17 @@
 
 import os
 from io import BytesIO
-from typing import TypedDict, Optional
+from typing import TypedDict
 
 import numpy as np
 import requests
 from dotenv import load_dotenv
 from PIL import Image
-from typing import TypedDict
 
 
 class NotificationData(TypedDict):
     message: str
-    image: Optional[np.ndarray]
+    image: np.ndarray | None
 
 
 class LineNotifier:
@@ -37,27 +36,31 @@ def __init__(self, line_token: str | None = None):
                 'LINE_NOTIFY_TOKEN not provided or in environment variables.',
             )
 
-    def send_notification(self, data: NotificationData) -> int:
+    def send_notification(
+        self,
+        message: str,
+        image: np.ndarray | None = None,
+    ) -> int:
         """
         Sends a notification via LINE Notify, optionally including an image.
 
         Args:
-            data (NotificationData): The notification data including message
-                and optional image.
+            message (str): The message to send.
+            label (Optional[str]): The label of the image_name.
+            image (Optional[np.ndarray]): The image to send with the message.
+                Defaults to None.
 
         Returns:
             response.status_code (int): The status code of the response.
         """
         headers = {'Authorization': f"Bearer {self.line_token}"}
-        payload = {'message': data['message']}
+        payload = {'message': message}
         files = {}
 
-        if data['image'] is not None:
-            if isinstance(data['image'], bytes):
+        if image is not None:
+            if isinstance(image, bytes):
                 # Convert bytes to NumPy array
-                image = np.array(Image.open(BytesIO(data['image'])))
-            else:
-                image = data['image']
+                image = np.array(Image.open(BytesIO(image)))
             image_pil = Image.fromarray(image)
             buffer = BytesIO()
             image_pil.save(buffer, format='PNG')
@@ -85,11 +88,7 @@ def main():
     message = 'Hello, LINE Notify!'
     # Create a dummy image for testing
     image = np.zeros((100, 100, 3), dtype=np.uint8)
-    data: NotificationData = {
-        'message': message,
-        'image': image,
-    }
-    response_code = notifier.send_notification(data)
+    response_code = notifier.send_notification(message, image=image)
     print(f"Response code: {response_code}")
 
 
diff --git a/tests/line_notifier_test.py b/tests/line_notifier_test.py
new file mode 100644
index 0000000..928c4b2
--- /dev/null
+++ b/tests/line_notifier_test.py
@@ -0,0 +1,97 @@
+from __future__ import annotations
+
+import unittest
+from io import BytesIO
+from unittest.mock import MagicMock
+from unittest.mock import patch
+
+import numpy as np
+from PIL import Image
+
+from src.line_notifier import LineNotifier
+
+
+class TestLineNotifier(unittest.TestCase):
+    def setUp(self):
+        self.line_token = 'test_token'
+        self.message = 'Test Message'
+        self.image = np.zeros((100, 100, 3), dtype=np.uint8)
+        self.notifier = LineNotifier(line_token=self.line_token)
+
+    @patch.dict('os.environ', {'LINE_NOTIFY_TOKEN': 'test_env_token'})
+    def test_init_with_env_token(self):
+        notifier = LineNotifier()
+        self.assertEqual(notifier.line_token, 'test_env_token')
+
+    def test_init_with_provided_token(self):
+        notifier = LineNotifier(line_token='provided_token')
+        self.assertEqual(notifier.line_token, 'provided_token')
+
+    def test_init_without_token(self):
+        with self.assertRaises(ValueError):
+            LineNotifier(line_token=None)
+
+    @patch('src.line_notifier.requests.post')
+    def test_send_notification_without_image(self, mock_post):
+        mock_response = MagicMock()
+        mock_response.status_code = 200
+        mock_post.return_value = mock_response
+
+        status_code = self.notifier.send_notification(self.message)
+        self.assertEqual(status_code, 200)
+        mock_post.assert_called_once_with(
+            'https://notify-api.line.me/api/notify',
+            headers={'Authorization': f'Bearer {self.line_token}'},
+            params={'message': self.message},
+        )
+
+    @patch('src.line_notifier.requests.post')
+    def test_send_notification_with_image(self, mock_post):
+        mock_response = MagicMock()
+        mock_response.status_code = 200
+        mock_post.return_value = mock_response
+
+        status_code = self.notifier.send_notification(self.message, self.image)
+        self.assertEqual(status_code, 200)
+        mock_post.assert_called_once()
+        args, kwargs = mock_post.call_args
+        self.assertIn('files', kwargs)
+        self.assertIn('imageFile', kwargs['files'])
+
+        # Check if the image is correctly converted and sent
+        image_file = kwargs['files']['imageFile']
+        self.assertEqual(image_file[0], 'image.png')
+        self.assertEqual(image_file[2], 'image/png')
+        image = Image.open(image_file[1])
+        self.assertTrue(np.array_equal(np.array(image), self.image))
+
+    @patch('src.line_notifier.requests.post')
+    def test_send_notification_with_bytes_image(self, mock_post):
+        mock_response = MagicMock()
+        mock_response.status_code = 200
+        mock_post.return_value = mock_response
+
+        buffer = BytesIO()
+        Image.fromarray(self.image).save(buffer, format='PNG')
+        buffer.seek(0)
+        image_bytes = buffer.read()
+
+        status_code = self.notifier.send_notification(
+            self.message, image_bytes,
+        )
+        self.assertEqual(status_code, 200)
+        mock_post.assert_called_once()
+        args, kwargs = mock_post.call_args
+        self.assertIn('files', kwargs)
+        self.assertIn('imageFile', kwargs['files'])
+
+        # Check if the image is correctly converted and sent
+        image_file = kwargs['files']['imageFile']
+        self.assertEqual(image_file[0], 'image.png')
+        self.assertEqual(image_file[2], 'image/png')
+        image = Image.open(image_file[1])
+        self.assertTrue(np.array_equal(np.array(image), self.image))
+
+
+if __name__ == '__main__':
+    unittest.main()