diff --git a/lib/classes/Variables.test.js b/lib/classes/Variables.test.js
index dce54473d..9de84e864 100644
--- a/lib/classes/Variables.test.js
+++ b/lib/classes/Variables.test.js
@@ -263,7 +263,7 @@ describe('Variables', () => {
       const makeAsyncLoadJs = () => {
         const SUtils = new Utils();
         const tmpDirPath = testUtils.getTmpDirPath();
-        const fileContent = `
+        const fileContent = `'use strict';
 let i = 0
 const str = () => new Promise((resolve) => {
   setTimeout(() => {