Update param name, add test for `e.which = 2`

spec/javascripts/merge_request_tabs_spec.js

@@ -84,9 +84,9 @@ require('vendor/jquery.scrollTo');
         const tabUrl = $(commitsLink).attr('href');
 
         spyOn($.fn, 'attr').and.returnValue(tabUrl);
-        spyOn(window, 'open').and.callFake(function (url, name) {
+        spyOn(window, 'open').and.callFake(function (url, target) {
           expect(url).toEqual(tabUrl);
-          expect(name).toEqual('_blank');
+          expect(target).toEqual('_blank');
         });
 
         this.class.clickTab({
@@ -96,6 +96,23 @@ require('vendor/jquery.scrollTo');
           stopImmediatePropagation: function () {}
         });
       });
+      it('opens page tab in a new browser tab with Middle-click - Mac/PC', function () {
+        const commitsLink = '.commits-tab li a';
+        const tabUrl = $(commitsLink).attr('href');
+
+        spyOn($.fn, 'attr').and.returnValue(tabUrl);
+        spyOn(window, 'open').and.callFake(function (url, target) {
+          expect(url).toEqual(tabUrl);
+          expect(target).toEqual('_blank');
+        });
+
+        this.class.clickTab({
+          metaKey: false,
+          ctrlKey: false,
+          which: 2,
+          stopImmediatePropagation: function () {}
+        });
+      });
     });
 
     describe('#setCurrentAction', function () {