add user cant follow himself validation

app/models/user_follow.rb

@@ -1,4 +1,12 @@
 class UserFollow < ApplicationRecord
   belongs_to :follower, class_name: 'User'
   belongs_to :followed, class_name: 'User'
+
+  validate :followed, :user_cant_follow_himself
+
+  private
+
+  def user_cant_follow_himself
+    errors.add(:followed, 'can\'t follow himself') if follower_id == followed_id
+  end
 end

spec/factories/users.rb

@@ -1,5 +1,8 @@
 FactoryBot.define do
   factory :user do
-    username { Faker::Internet.username.gsub(/[^0-9a-z ]/i, '') }
+    username {
+      Faker::Internet.username[0..14]
+        .gsub(/[^0-9a-z ]/i, '')
+    }
   end
 end

spec/models/user_follow_spec.rb

@@ -0,0 +1,14 @@
+require 'rails_helper'
+
+RSpec.describe UserFollow, type: :model do
+  describe 'validations' do
+    context 'and user try to follow her-self' do
+      it 'raise error' do
+        user = create(:user)
+        user_follow = build(:user_follow, follower_id: user.id, followed_id: user.id)
+
+        expect(user_follow).to_not be_valid
+      end
+    end
+  end
+end