Improve tests for different localStorage-not-accessible situations

Run all of the existing tests to check behavior when localStorage is not
accessible, for the case where accessing `window.localStorage` throws.

The previous tests for this situation only tested the behavior of the
service constructor.

src/sidebar/test/local-storage-test.js

@@ -3,6 +3,28 @@
 var angular = require('angular');
 var service = require('../local-storage');
 
+function windowWithLocalStoragePropertyThatThrows() {
+  var win = {};
+  Object.defineProperty(win, 'localStorage', {
+    get() {
+      throw Error('denied');
+    },
+  });
+  return win;
+}
+
+function windowWithLocalStorageMethodsThatThrow() {
+  var throwErr = sinon.stub.throws(new Error('Denied'));
+
+  return {
+    localStorage: {
+      getItem: throwErr,
+      removeItem: throwErr,
+      setItem: throwErr,
+    },
+  };
+}
+
 describe('sidebar.localStorage', () => {
   var fakeWindow;
 
@@ -11,34 +33,17 @@ describe('sidebar.localStorage', () => {
       .service('localStorage', service)
   );
 
-  context('when accessing localStorage throws an Error', () => {
-    it('returns the fallback implementation', () => {
-      var badWindow = {};
-      var fakeWindow = {};
-
-      Object.defineProperty(badWindow, 'localStorage', {
-        get: () => {
-          throw Error('denied');
-        },
-      });
-
-      var prototypes = [badWindow, fakeWindow]
-          .map(service)
-          .map(Object.getPrototypeOf)
-      ;
-      assert.strictEqual(prototypes[0], prototypes[1]);
-    });
-  });
-
+  [
+    windowWithLocalStorageMethodsThatThrow(),
+    windowWithLocalStoragePropertyThatThrows(),
+  ].forEach(($window) => {
     context('when browser localStorage is *not* accessible', () => {
       var localStorage = null;
       var key = null;
 
       beforeEach(() => {
         angular.mock.module('h', {
-        $window: {
-          localStorage: {},
-        },
+          $window,
         });
       });
 
@@ -71,6 +76,7 @@ describe('sidebar.localStorage', () => {
         assert.deepEqual(actual, data);
       });
     });
+  });
 
   context('when browser localStorage is accessible', () => {
     var localStorage;