diff --git a/swh/loader/package/nixguix/tests/test_nixguix.py b/swh/loader/package/nixguix/tests/test_nixguix.py
--- a/swh/loader/package/nixguix/tests/test_nixguix.py
+++ b/swh/loader/package/nixguix/tests/test_nixguix.py
@@ -59,6 +59,15 @@
         (TargetType.REVISION, b"evaluation")
     ],
 ):
+    """The `evaluation` branch is allowed to be unresolvable as it's possible at current
+    nixguix visit time, it was not visited yet (the git loader is in charge of its visit
+    for now).
+
+    For more details, check the swh.loader.package.nixguix.NixGuixLoader.extra_branches
+    docstring.
+
+    """
+
     check_snapshot_full(snapshot, storage, allowed_empty)
 
     assert isinstance(snapshot, Snapshot)
@@ -66,7 +75,7 @@
     revision_ids = []
     for name, branch in snapshot.branches.items():
         if name == b"evaluation":
-            continue  # skipping that particular branch
+            continue  # skipping that particular branch (cf. docstring above)
         if branch.target_type == TargetType.REVISION:
             revision_ids.append(branch.target)