does not allow user to vote for his own post - ruby-on-rails

Question

I have three models User, Post, Vote
I need to doesn't allow user to vote for his own post.
How I can make this in my models and test this in Rspec?
Post Model:
class Post < ActiveRecord::Base
attr_accessible :title, :main_text, :video, :photo, :tag
validates :title, presence: true, length: {minimum: 1, maximum: 200}
validates :main_text, presence: true, length: {minimum: 1}
belongs_to :user
has_many :votes
end
User Model:
class User < ActiveRecord::Base
attr_accessible :name, :email, :bio
has_many :posts
has_many :votes
validates :name, presence: true, length: {minimum: 1, maximum: 120}
validates :email, presence: true, length: {minimum: 5, maximum: 250}, uniqueness: true,
format: {:with => /^([^#\s]+)#((?:[-a-z0-9]+\.)+[a-z]{2,})$/i}
end
Vote model:
class Vote < ActiveRecord::Base
attr_accessible :user_id, :post_id, :units
belongs_to :user
belongs_to :post
validates :post_id, uniqueness: {scope: :user_id} #does not allow user to vote for the same post twice
end
My spec test for Vote:
require 'spec_helper'
describe Vote do
it "does not allow user to vote for the same post twice" do
user = User.create(name: "Nik", email: "nik#google.com" )
post = Post.create(title: "New Post", main_text: "Many, many, many...")
vote1 = Vote.create(user_id: user.id, post_id: post.id)
vote1.errors.should be_empty
vote2 = Vote.create(user_id: user.id, post_id: post.id)
vote2.errors.should_not be_empty
end
it "does not allow user to vote for his own post" do
user = User.create(name:"Nik", email:"a#a.ru")
post = Post.create(user_id: user.id, title: "New Post", main_text: "Many, many, many...")
vote1 = Vote.create(user_id: user.id, post_id: post.id)
vote1.errors.should_not be_empty
end
end

Answer 1

I've not tested the following code so it could not work or even kill your cats but try with a custom validation with add an error if the vote's user is the same of the post's user.
Note I return if the user or the post are nil for obvius reasons.
# In your vote model
validate :users_cant_vote_their_posts
def users_cant_vote_their_posts
return if user.nil? or post.nil?
if user_id == post.user_id
errors[:base] = "A user can't vote their posts"
end
end
EDIT: Here a possible test, here I'm using FactoryGirl to generate votes. Again this code is not tested (sorry for the pun)
describe Vote do
subject { vote }
let!(:vote) { FactoryGirl.build(:vote) }
it 'from factory should be valid' do
should be_valid
end
context 'when user try to double vote' do
before do
# Create another vote from user to post
FactoryGirl.create(:vote, :user => vote.user, :post => vote.post)
end
it { should_not be_valid }
end
context 'when user try to vote his posts' do
before do
# Set the user whom voted to the post's owner
vote.user = vote.post.user
end
it { should_not be_valid }
end
end

Answer 2

I don't know ruby, but you should check whether the user signed in matches the user that made the post. And if it does, deny the request to vote.
Sorry if this is not helpful :)