diff --git a/swh/loader/core/loader.py b/swh/loader/core/loader.py
--- a/swh/loader/core/loader.py
+++ b/swh/loader/core/loader.py
@@ -70,9 +70,14 @@
     """
 
     def __init__(
-        self, logging_class: Optional[str] = None,
+        self,
+        logging_class: Optional[str] = None,
+        config: Optional[Dict[str, Any]] = None,
     ):
-        self.config = load_from_envvar(DEFAULT_CONFIG)
+        if config:
+            self.config = config
+        else:
+            self.config = load_from_envvar(DEFAULT_CONFIG)
 
         self.storage = get_storage(**self.config["storage"])