diff --git a/.gitignore b/.gitignore
index 55e6cc84408f4a6e466147637b1d368506eef40b..d3edf61edcee2368bc7a7b18261da8a35c1bcb56 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,7 +8,7 @@
 *.pyc
 *.egg-info
 .nfs*
-.coverage
+.coverage*
 *.DS_Store
 .envrc
 coverage.xml
diff --git a/src/ptbench/data/montgomery/__init__.py b/src/ptbench/data/montgomery/__init__.py
index 4334180592ffca7cbbcd299e901d472418e5cebd..fd65f24dbde588d9958b90a488ea56cc4111496e 100644
--- a/src/ptbench/data/montgomery/__init__.py
+++ b/src/ptbench/data/montgomery/__init__.py
@@ -40,12 +40,18 @@ _protocols = [
     importlib.resources.files(__name__).joinpath("fold_9.json.bz2"),
 ]
 
-_root_path = load_rc().get("datadir.montgomery", os.path.realpath(os.curdir))
+_root_path = None
 
 
 def _raw_data_loader(sample):
+    # hack to allow tests to change "datadir.montgomery"
+    global _root_path
+    _root_path = _root_path or load_rc().get(
+        "datadir.montgomery", os.path.realpath(os.curdir)
+    )
+
     return dict(
-        data=load_pil_baw(os.path.join(_root_path, sample["data"])),
+        data=load_pil_baw(os.path.join(_root_path, sample["data"])),  # type: ignore
         label=sample["label"],
     )