ruby-on-rails - NoMethodError: 外部キーの未定義のメソッド - Rails 4

Question

これは私が得たエラーです。

UserFriendshipTest#test_that_creating_a_friendship_works_without_raising_an_exception:
NoMethodError: undefined method `friend' for #<UserFriendshipTest:0x2947dd0>
    test/models/user_friendship_test.rb:9:in `block (2 levels) in <class:UserFriendshipTest>'
    test/models/user_friendship_test.rb:8:in `block in <class:UserFriendshipTest>'

これは私の user_friendship_test.rb コードです。

require 'test_helper'
class UserFriendshipTest < ActiveSupport::TestCase
    should belong_to(:user)
    should belong_to(:friend)

    test "that creating a friendship works without raising an exception" do
        assert_nothing_raised do 
            UserFriendship.create user: users(:brijesh), friend: friend(:neha)
        end
    end
end     

そして、これは私の user_friendship.rb です

class UserFriendship < ActiveRecord::Base
    belongs_to :user
    belongs_to :friend, class_name: "User", foreign_key: "friend_id"
end