Validate uniquness of api_key.

app/models/api_key.rb

@@ -2,6 +2,7 @@ class ApiKey < ActiveRecord::Base
   belongs_to :user
   belongs_to :created_by, class_name: User
 
+  validates :user_id, uniqueness: true
   validates_presence_of :key
 
   def regenerate!(updated_by)

spec/models/api_key_spec.rb

@@ -3,14 +3,18 @@ require 'rails_helper'
 require_dependency 'api_key'
 
 describe ApiKey do
+  let(:user) { Fabricate(:user) }
+
   it { is_expected.to belong_to :user }
   it { is_expected.to belong_to :created_by }
-
   it { is_expected.to validate_presence_of :key }
 
-  skip 'validates uniqueness of user_id' do
-    Fabricate(:api_key)
-    is_expected.to validate_uniqueness_of(:user_id)
+  it 'validates uniqueness of user_id' do
+    Fabricate(:api_key, user: user)
+    api_key = Fabricate.build(:api_key, user: user)
+
+    expect(api_key.save).to eq(false)
+    expect(api_key.errors).to include(:user_id)
   end
 
 end