Refactor download_url test into TestDownloadUrl class

Refactor test for download_url to use a class-based structure and improve hash validation.

Signed-off-by: Enoch Mok <65853622+e-mny@users.noreply.github.com>

Author: e-mny

tests/test_utils.py

@@ -183,32 +183,35 @@ def skip_if_downloading_fails():
 
         raise rt_e
 
-
-SAMPLE_TIFF = (
-    https://huggingface.co/datasets/MONAI/testing_data/resolve/main/CMU-1.tiff
-)
-
+SAMPLE_TIFF = "https://huggingface.co/datasets/MONAI/testing_data/resolve/main/CMU-1.tiff"
 SAMPLE_TIFF_HASH = "73a7e89bc15576587c3d68e55d9bf92f09690280166240b48ff4b48230b13bcd"
 SAMPLE_TIFF_HASH_TYPE = "sha256"
 
-def test_download_url():
-    with tempfile.TemporaryDirectory() as tempdir:
-        # successful download with correct hash
-        download_url(
-            url=SAMPLE_TIFF,
-            filepath=os.path.join(tempdir, "model.tiff"),
-            hash_val=SAMPLE_TIFF_HASH,
-            hash_type=SAMPLE_TIFF_HASH_TYPE,
-        )
 
-        # fails with wrong hash
-        with unittest.assertRaises(RuntimeError):
-            download_url(
-                url=SAMPLE_TIFF,
-                filepath=os.path.join(tempdir, "model_bad.tiff"),
-                hash_val="wrong_hash",
-                hash_type=SAMPLE_TIFF_HASH_TYPE,
-            )
+class TestDownloadUrl(unittest.TestCase):
+    """Exercise ``download_url`` success and hash-mismatch paths."""
+
+    def test_download_url(self):
+        """Download a sample TIFF and validate hash handling.
+
+        Raises:
+            RuntimeError: When the downloaded file's hash does not match.
+        """
+        with tempfile.TemporaryDirectory() as tempdir:
+            with skip_if_downloading_fails():
+                download_url(
+                    url=SAMPLE_TIFF,
+                    filepath=os.path.join(tempdir, "model.tiff"),
+                    hash_val=SAMPLE_TIFF_HASH,
+                    hash_type=SAMPLE_TIFF_HASH_TYPE,
+                )
+            with self.assertRaises(RuntimeError):
+                download_url(
+                    url=SAMPLE_TIFF,
+                    filepath=os.path.join(tempdir, "model_bad.tiff"),
+                    hash_val="0" * 64,
+                    hash_type=SAMPLE_TIFF_HASH_TYPE,
+                )
 
 def test_pretrained_networks(network, input_param, device):
     with skip_if_downloading_fails():