diff --git a/tests/git-hooks-no-python-leak/devenv.nix b/tests/git-hooks-no-python-leak/devenv.nix
new file mode 100644
index 000000000..4d0fb8ab7
--- /dev/null
+++ b/tests/git-hooks-no-python-leak/devenv.nix
@@ -0,0 +1,12 @@
+# Assert that the pre-commit package does not leak its dependencies into the environment.
+{
+  git-hooks.hooks.nixfmt-rfc-style.enable = true;
+
+  enterTest = ''
+    if [ -n "$PYTHONPATH" ]; then
+      echo "PYTHONPATH is non-empty: $PYTHONPATH" >&2
+      echo "The pre-commit package is leaking its dependencies into the environment." >&2
+      exit 1
+    fi
+  '';
+}