made set_role only accept saved roles

app/models/role.rb

@@ -1,3 +1,4 @@
 class Role < ActiveRecord::Base
 	has_and_belongs_to_many :users
+	validates :name, uniqueness: true
 end

app/models/user.rb

@@ -27,6 +27,8 @@ def User.encrypt(token)
   end
 
   def set_role(role)
+  	if Role.find(role.id)
+  		self.roles << role  		
   end
 
 

spec/models/role_spec.rb

@@ -12,12 +12,19 @@
   	describe "it should show a users roles" do
   		let(:user_id) do
   			user = FactoryGirl.create(:user)
-  			user.roles << role
+  			user.set_role(role)
   			user.save
   			user.id
   		end
 
   		specify { expect(User.find(user_id).roles).to eq [role] }
+  		specify { expect(role.users).to eq [User.find(user_id)] }
   	end
-end
+
+  	describe "creating a role with a name that already exists" do
+  		let(:duplicate_role) {Role.new(name: role.name)}
+  		specify { expect(duplicate_role).not_to be_valid }
+  	end
+
+end		
 

spec/models/user_spec.rb

@@ -9,6 +9,7 @@
 	it { should respond_to(:email) }
 	it { should respond_to(:encrypted_password)}
 	it { should respond_to(:remember_token)}
+	it { should respond_to(:roles) }
 
 	it { should be_valid }