add exception handling in helper functions

tests/helper_functions.py

@@ -3,6 +3,13 @@
 import requests
 
 
+class HTTPError(Exception):
+    def __init__(self, status_code, message):
+        self.status_code = status_code
+        self.message = message
+        super().__init__(f"HTTPError {status_code}: {message}")
+
+
 def download_test_data(nexus_url, filename):
     local_directory = "./tests/data"
 
@@ -15,7 +22,8 @@ def download_test_data(nexus_url, filename):
     if not os.path.exists(local_file_path):
         session = requests.Session()
         response = session.get(nexus_url)
-        # response.raise_for_status()
+        if response.status_code != 200:
+            raise HTTPError(response.status_code, "Failed to download data.")
         # Save the downloaded data to the local file
         with open(local_file_path, "wb") as f:
             f.write(response.content)