diff --git a/mailpoet/RoboFile.php b/mailpoet/RoboFile.php
index 8a01f5666d..70c6e4d560 100644
--- a/mailpoet/RoboFile.php
+++ b/mailpoet/RoboFile.php
@@ -371,6 +371,7 @@ class RoboFile extends \Robo\Tasks {
     $command = join(' ', [
       './node_modules/.bin/mocha',
       '-r tests/javascript-newsletter-editor/mocha-test-helper.js',
+      '-r tests/javascript-newsletter-editor/mocha-chai.mjs',
       'tests/javascript-newsletter-editor/testBundles/**/*.js',
       '--exit',
     ]);
diff --git a/mailpoet/tests/javascript-newsletter-editor/mocha-chai.mjs b/mailpoet/tests/javascript-newsletter-editor/mocha-chai.mjs
new file mode 100644
index 0000000000..e502db9255
--- /dev/null
+++ b/mailpoet/tests/javascript-newsletter-editor/mocha-chai.mjs
@@ -0,0 +1,8 @@
+import * as chai from 'chai';
+import sinonChai from 'sinon-chai';
+import chaiJq from 'chai-jq';
+
+chai.use(sinonChai);
+chai.use(chaiJq);
+
+global.expect = chai.expect;
diff --git a/mailpoet/tests/javascript-newsletter-editor/mocha-test-helper.js b/mailpoet/tests/javascript-newsletter-editor/mocha-test-helper.js
index a79a0c7990..384681c55b 100644
--- a/mailpoet/tests/javascript-newsletter-editor/mocha-test-helper.js
+++ b/mailpoet/tests/javascript-newsletter-editor/mocha-test-helper.js
@@ -1,16 +1,9 @@
-var chai = require('chai');
 var sinon = require('sinon');
-var sinonChai = require('sinon-chai');
-var chaiJq = require('chai-jq');
 var _ = require('underscore');
 var { JSDOM } = require('jsdom');
 var URL = require('url').URL;
 var nodeCrypto = require('crypto');
 
-chai.use(sinonChai);
-chai.use(chaiJq);
-
-global.expect = chai.expect;
 global.sinon = sinon;
 global.URL = URL;