The Tor Browser / file revision

 function numClosedTabs()

   SessionStore.getClosedTabCount(window);

 function isUndoCloseEnabled() {

   updateTabContextMenu();

   return !document.getElementById("context_undoCloseTab").disabled;

 }

 function test() {

   waitForExplicitFinish();

   gPrefService.setIntPref("browser.sessionstore.max_tabs_undo", 0);

   gPrefService.clearUserPref("browser.sessionstore.max_tabs_undo");

   is(numClosedTabs(), 0, "There should be 0 closed tabs.");

   ok(!isUndoCloseEnabled(), "Undo Close Tab should be disabled.");

   var tab = gBrowser.addTab("http://mochi.test:8888/");

   var browser = gBrowser.getBrowserForTab(tab);

   browser.addEventListener("load", function() {

     browser.removeEventListener("load", arguments.callee, true);

     gBrowser.removeTab(tab);

     ok(isUndoCloseEnabled(), "Undo Close Tab should be enabled.");

     finish();

   }, true);

 }