test(alert_tab): basic test skeleton

I created this test by misstake. But instead of deleting it I thought it
might be good to keep it to make it easier to add tests for the alert
tab

public/app/features/alerting/specs/alert_tab_specs.ts

+import {describe, beforeEach, it, sinon, expect, angularMocks} from 'test/lib/common';
+
+import {AlertTabCtrl} from '../alert_tab_ctrl';
+import helpers from '../../../../test/specs/helpers';
+
+describe('AlertTabCtrl', () => {
+  var $scope = {
+    ctrl: {}
+  };
+
+  describe('with null parameters', () => {
+    it('can be created', () => {
+      var alertTab = new AlertTabCtrl($scope, null, null, null, null, null, null, null);
+
+      expect(alertTab).to.not.be(null);
+    });
+  });
+});
+
+