diff --git a/package.json b/package.json
index 6692a2a..bd10223 100644
--- a/package.json
+++ b/package.json
@@ -47,7 +47,8 @@
     "husky": "^9.0.6",
     "jest": "^29.1.2",
     "jison": "^0.4.18",
-    "onchange": "^7.1.0"
+    "onchange": "^7.1.0",
+    "mock-fs": "^5.3.0",
   },
   "funding": {
     "type": "liberapay",