diff --git a/tests/test_subdir.py b/tests/test_subdir.py
index e200710c..6c183c98 100644
--- a/tests/test_subdir.py
+++ b/tests/test_subdir.py
@@ -7,6 +7,7 @@ from os.path import abspath, dirname
 import pytest
 from repo2docker.app import Repo2Docker
 
+# This is the path to the repo2docker git repository that this file exists in.
 repo_path = dirname(dirname(abspath(__file__)))