add test case with data on server

tests/test_flip_image.py

+import os
 import unittest
 
 import numpy as np
@@ -17,10 +18,30 @@ class FlipImageTestCase(unittest.TestCase):
         with self.assertRaises(AssertionError):
             flip_image(np.array([1, 2, 3, 4]))
 
+    def test_flip_image_on_server(self):
+        """test flip image on server"""
+        image_input = np.load(
+            os.path.join(
+                os.environ["UNIT_TEST_DATA_ROOT"],
+                "csst_proto/test_flip/input/image.txt",
+            )
+        )
+        image_answer = np.load(
+            os.path.join(
+                os.environ["UNIT_TEST_DATA_ROOT"],
+                "csst_proto/test_flip/answer/flipped_image.txt",
+            )
+        )
+        self.assertIs(
+            flip_image(image_input),
+            image_answer,
+            "Test flip image on server failed",
+        )
+
     def test_flip_multiple_images_mp(self):
         """test flip multiple images with multiprocessing"""
         n_jobs = 10
-        imgs = [read_default_image() for i_job in range(n_jobs)]
+        imgs = [read_default_image() for _ in range(n_jobs)]
         flipped_imgs = flip_multiple_images_mp(imgs, n_jobs)
         for i_job in range(n_jobs):
             self.assertTrue(np.all(flipped_imgs[i_job] == np.array([[4, 3], [2, 1]])))
@@ -28,7 +49,7 @@ class FlipImageTestCase(unittest.TestCase):
     def test_flip_multiple_images_jl(self):
         """test flip multiple images with joblib"""
         n_jobs = 10
-        imgs = [read_default_image() for i_job in range(n_jobs)]
+        imgs = [read_default_image() for _ in range(n_jobs)]
         flipped_imgs = flip_multiple_images_jl(imgs, n_jobs)
         for i_job in range(n_jobs):
             self.assertTrue(np.all(flipped_imgs[i_job] == np.array([[4, 3], [2, 1]])))