All the assignment done, but no optionals

From line 876 in the development log you can see that there are 5 users
created. All of them have post just one  post. Each post has 1 or more
comment from the users created and each post belong to a category.

Category now has: has_many categories
Post now has: has_many post_categories

The paths for post have been created, and an exception added on destroy