adding the relationship model validations in relationship.rb listing 11.8
a test for user.followed_users attributes in user_spec.rb listing 11.9
adding the User model followed association in user.rb listing 11.10
test for some 'following' ustility methods listing 11.11
the following? and follow! utility methods in user.rb
a test for unfollowing a user in user_spec.rb listing 11.13
unfollowing a user by destroying a user relationship
testing for reverse relationships in user_spec.rb listing 11.15
implementing the user.followers using reverse relationships in user.rb lising 11.16