Place MocktailDesigner in test/models/drink_designer.rb

Since `MocktailDesigner` inherits `DrinkDesigner` and can not be used
alone.

activerecord/test/cases/reflection_test.rb

@@ -25,7 +25,6 @@
 require "models/department"
 require "models/cake_designer"
 require "models/drink_designer"
-require "models/mocktail_designer"
 require "models/recipe"
 
 class ReflectionTest < ActiveRecord::TestCase

activerecord/test/models/drink_designer.rb

@@ -3,3 +3,6 @@
 class DrinkDesigner < ActiveRecord::Base
   has_one :chef, as: :employable
 end
+
+class MocktailDesigner < DrinkDesigner
+end

activerecord/test/models/mocktail_designer.rb

@@ -1,4 +0,0 @@
-# frozen_string_literal: true
-
-class MocktailDesigner < DrinkDesigner
-end