Fix intermittent JS test failure (Fixes #14319) (#14321)

tests/unit/spec/base/datalayer-begincheckout.js

@@ -75,7 +75,7 @@ describe('datalayer-begincheckout.es6.js', function () {
         });
 
         afterEach(function () {
-            window.dataLayer = [];
+            delete window.dataLayer;
         });
 
         it('will append the begin_checkout event to the dataLayer', function () {

tests/unit/spec/base/datalayer-productdownload.js

@@ -300,7 +300,9 @@ describe('TrackProductDownload.handleLink', function () {
     const download_button = `<a href="https://download.mozilla.org/?product=firefox-latest-ssl&amp;os=win64&amp;lang=en-CA" id="download-button-primary" class="mzp-c-button mzp-t-product c-download-button">Download Now</a>`;
 
     beforeEach(function () {
-        window.dataLayer = [];
+        // stub out google tag manager
+        window.dataLayer = sinon.stub();
+        window.dataLayer.push = sinon.stub();
 
         document.body.insertAdjacentHTML('beforeend', download_button);
         const downloadButton = document.getElementById(
@@ -318,7 +320,6 @@ describe('TrackProductDownload.handleLink', function () {
 
     afterEach(function () {
         document.getElementById('download-button-primary').remove();
-        window.dataLayer = [];
     });
 
     it('should call the full chain of functions', function () {

tests/unit/spec/products/vpn/invite.js

@@ -83,6 +83,10 @@ describe('WaitListForm', function () {
         </div>`;
 
         document.body.insertAdjacentHTML('beforeend', form);
+
+        // stub out google tag manager
+        window.dataLayer = sinon.stub();
+        window.dataLayer.push = sinon.stub();
     });
 
     afterEach(function () {