Added role-specifics to post API tests (#9058)

refs #9043

- this is preparation for adding Author-specific tests later
  - the changes the posts_spec.js, so that all the tests are inside an "As Owner" describe block, similar to the users_spec.js
- Added new util for creating a specific post
  - This will make it easier to do routing tests on the post model in future
  - Our `index.js` file in test/utils really needs a bit of love 🙈
- Also added all the framework for author role tests in post_spec.js
- Added a single test, showing we can edit posts, including author_id

core/test/utils/index.js

@@ -40,6 +40,7 @@ var Promise = require('bluebird'),
     setup,
     doAuth,
     createUser,
+    createPost,
     login,
     togglePermalinks,
     startGhost,
@@ -679,6 +680,20 @@ createUser = function createUser(options) {
         });
 };
 
+createPost = function createPost(options) {
+    var post = DataGenerator.forKnex.createPost(options.post);
+
+    if (options.author) {
+        post.author_id = options.author.id;
+    }
+
+    return db.knex('posts')
+        .insert(post)
+        .then(function () {
+            return post;
+        });
+};
+
 login = function login(request) {
     // CASE: by default we use the owner to login
     if (!request.user) {
@@ -857,6 +872,7 @@ module.exports = {
     setup: setup,
     doAuth: doAuth,
     createUser: createUser,
+    createPost: createPost,
     login: login,
     togglePermalinks: togglePermalinks,