diff -r 000000000000 -r 6474c204b198 browser/metro/base/tests/mochitest/browser_tabs.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/metro/base/tests/mochitest/browser_tabs.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,72 @@
+// -*- Mode: js2; tab-width: 2; indent-tabs-mode: nil; js2-basic-offset: 2; js2-skip-preprocessor-directives: t; -*-
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+let mockTab = function(aName, aIsClosing) {
+  this.name = aName;
+  this.isClosing = aIsClosing;
+};
+
+mockTab.prototype = {
+  get chromeTab () {
+    let getAttribute = () => this.isClosing;
+    return {
+      hasAttribute: getAttribute
+    }
+  }
+};
+
+let getMockBrowserTabs = function(aTestTabs, aSelected) {
+  let result = {
+    _tabs: aTestTabs,
+    _selectedTab: aTestTabs[aSelected || 0],
+    getTabAtIndex: function(i) this._tabs[i]
+  };
+
+  return [result, Browser.getNextTab.bind(result)];
+};
+
+gTests.push({
+  desc: "Test Browser.getNextTab",
+  run: function() {
+    let [lonlyTab, fakeGetNextTab] = getMockBrowserTabs(
+      [new mockTab("a", false)]);
+
+    ok(fakeGetNextTab(lonlyTab._selectedTab) == null, "null when only 1 tab left");
+    ok(fakeGetNextTab(new mockTab("x", false)) == null, "null when tab doesnt exist");
+
+    let [twoTabs, fakeGetNextTab] = getMockBrowserTabs(
+      [new mockTab("a", false), new mockTab("b", false)]);
+    ok(fakeGetNextTab(twoTabs._selectedTab).name == "b", "get next tab");
+    ok(fakeGetNextTab(twoTabs._tabs[1]).name == "a", "get selected tab");
+
+    let [twoTabsSecondSelected, fakeGetNextTab] = getMockBrowserTabs(
+      [new mockTab("a", false), new mockTab("b", false)], 1);
+    ok(fakeGetNextTab(twoTabsSecondSelected._selectedTab).name == "a", "get previous tab");
+
+    let [twoTabsOneClosing, fakeGetNextTab] = getMockBrowserTabs(
+      [new mockTab("a", false), new mockTab("b", true)]);
+    ok(fakeGetNextTab(twoTabsOneClosing._selectedTab) == null, "can't select closing tab");
+    ok(fakeGetNextTab(twoTabsOneClosing._tabs[1]).name == "a", "get previous tab");
+
+    let [twoTabsBothClosing, fakeGetNextTab] = getMockBrowserTabs(
+      [new mockTab("a", true), new mockTab("b", true)]);
+    ok(fakeGetNextTab(twoTabsBothClosing._selectedTab) == null, "can't select closing tab");
+    ok(fakeGetNextTab(twoTabsBothClosing._tabs[1]) == null, "can't select closing tab");
+
+    let [fiveTabsLastNotClosing, fakeGetNextTab] = getMockBrowserTabs(
+      [new mockTab("a", false), new mockTab("b", true), new mockTab("c", true), new mockTab("d", true), new mockTab("e", false)]);
+    ok(fakeGetNextTab(fiveTabsLastNotClosing._selectedTab).name == "e", "get next non-closing tab");
+
+    let [fiveTabsLastNotClosingLastSelected, fakeGetNextTab] = getMockBrowserTabs(
+      [new mockTab("a", false), new mockTab("b", true), new mockTab("c", true), new mockTab("d", true), new mockTab("e", false)], 4);
+    ok(fakeGetNextTab(fiveTabsLastNotClosingLastSelected._selectedTab).name == "a", "get previous non-closing tab");
+  }
+});
+
+function test() {
+  runTests();
+}