set activerecord whitelist_attributes to true

spec/models/users_project_spec.rb

@@ -6,6 +6,10 @@ describe UsersProject do
     it { should belong_to(:user) }
   end
 
+  describe "Mass assignment" do
+    it { should_not allow_mass_assignment_of(:project_id) }
+  end
+
   describe "Validation" do
     let!(:users_project) { create(:users_project) }