validate category user_id.

app/models/category.rb

@@ -10,6 +10,7 @@ class Category < ActiveRecord::Base
   has_many :category_featured_users
   has_many :featured_users, through: :category_featured_users, source: :user
 
+  validates_presence_of :user_id
   validates_presence_of :name
   validates_uniqueness_of :name
   validate :uncategorized_validator

spec/models/category_spec.rb

@@ -4,6 +4,7 @@ require 'spec_helper'
 
 describe Category do
 
+  it { should validate_presence_of :user_id }
   it { should validate_presence_of :name }
 
   it 'validates uniqueness of name' do