diff --git a/swh/loader/cvs/tests/test_loader.py b/swh/loader/cvs/tests/test_loader.py
--- a/swh/loader/cvs/tests/test_loader.py
+++ b/swh/loader/cvs/tests/test_loader.py
@@ -240,7 +240,7 @@
     repo_url += "/runbaby"  # CVS module name
 
     # Ask our cvsclient to connect via the 'cvs server' command
-    repo_url = "fake://" + repo_url[7:]
+    repo_url = f"fake://{repo_url[7:]}"
 
     loader = CvsLoader(
         swh_storage, repo_url, cvsroot_path=os.path.join(tmp_path, archive_name)
@@ -291,7 +291,7 @@
     repo_url += "/greek-tree"  # CVS module name
 
     # Ask our cvsclient to connect via the 'cvs server' command
-    repo_url = "fake://" + repo_url[7:]
+    repo_url = f"fake://{repo_url[7:]}"
 
     loader = CvsLoader(
         swh_storage, repo_url, cvsroot_path=os.path.join(tmp_path, archive_name)