Add initial tabbingIdentifier spec

spec/api-browser-window-spec.js

@@ -692,7 +692,7 @@ describe('BrowserWindow module', function () {
     })
   })
 
-  describe('"title-bar-style" option', function () {
+  describe('"titleBarStyle" option', function () {
     if (process.platform !== 'darwin') {
       return
     }
@@ -772,6 +772,20 @@ describe('BrowserWindow module', function () {
     })
   })
 
+  describe('"tabbingIdentifier" option', function () {
+    it('can be set on a window', function () {
+      w.destroy()
+      w = new BrowserWindow({
+        tabbingIdentifier: 'group1'
+      })
+      w.destroy()
+      w = new BrowserWindow({
+        tabbingIdentifier: 'group2',
+        frame: false
+      })
+    })
+  })
+
   describe('"web-preferences" option', function () {
     afterEach(function () {
       ipcMain.removeAllListeners('answer')