diff --git a/swh/loader/package/tests/common.py b/swh/loader/package/tests/common.py
index e8e2292..d83f2d8 100644
--- a/swh/loader/package/tests/common.py
+++ b/swh/loader/package/tests/common.py
@@ -1,83 +1,86 @@
 # Copyright (C) 2019  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 from os import path
 from urllib.parse import urlparse
 
 from swh.model.hashutil import hash_to_bytes, hash_to_hex
 
 
 DATADIR = path.join(path.abspath(path.dirname(__file__)), 'resources')
 
 
 def get_response_cb(request, context):
     """Mount point callback to fetch on disk the content of a request
 
     Args:
         request (requests.Request): Object requests
         context (requests.Context): Object holding requests metadata
                                     information (headers, etc...)
 
     Returns:
         File descriptor on the on disk file to read from the test context
 
     """
     url = urlparse(request.url)
     dirname = url.hostname  # pypi.org | files.pythonhosted.org
     # url.path: pypi/<project>/json -> local file: pypi_<project>_json
     filename = url.path[1:]
     if filename.endswith('/'):
         filename = filename[:-1]
     filename = filename.replace('/', '_')
     filepath = path.join(DATADIR, dirname, filename)
+    if not path.isfile(filepath):
+        context.status_code = 404
+        return None
     fd = open(filepath, 'rb')
     context.headers['content-length'] = str(path.getsize(filepath))
     return fd
 
 
 def decode_target(target):
     if not target:
         return target
     target_type = target['target_type']
 
     if target_type == 'alias':
         decoded_target = target['target'].decode('utf-8')
     else:
         decoded_target = hash_to_hex(target['target'])
 
     return {
         'target': decoded_target,
         'target_type': target_type
     }
 
 
 def check_snapshot(expected_snapshot, expected_branches, storage):
     """Check for snapshot match.
 
     Provide the hashes as hexadecimal, the conversion is done
     within the method.
 
     Args:
         expected_snapshot (Union[str, dict]): Either the snapshot
                                       identifier or the full
                                       snapshot
         expected_branches ([dict]): expected branches or nothing is
                                   the full snapshot is provided
 
     """
     if isinstance(expected_snapshot, dict) and not expected_branches:
         expected_snapshot_id = expected_snapshot['id']
         expected_branches = expected_snapshot['branches']
     else:
         expected_snapshot_id = expected_snapshot
 
     snap = storage.snapshot_get(hash_to_bytes(expected_snapshot_id))
     assert snap is not None
 
     branches = {
         branch.decode('utf-8'): decode_target(target)
         for branch, target in snap['branches'].items()
     }
     assert expected_branches == branches