shvets / design_patterns_in_ruby

# singleton-corrected.rb
 
# Trying to replcae Singleton pattern with interface inheritance and dependency injection.
# Now we can mock the singleton. 
 
# - Reduce hidden coupling;
# - Allow testability;
# - Allow subclassing;
# - Make construction and use flexible;
 
# 1. Rediefine singleton. 
 
class Singleton
  def operation
  end
end
 
class MySingleton < Singleton
  def operation
    puts "operation"
  end
end
 
# 2. Class that uses the singleton object (we should be able to set it up from outside).
 
class SingletonUser
  def initialize(singleton)
    @singleton = singleton
  end
 
  def do_something
    @singleton.operation
  end
 
end
 
# 3. Mock object for the singleton and the test
 
class MockSingleton < Singleton
 
  def operation
    puts "mock operation"
  end
 
end
 
class SingletonTest
  def test_singleton
    singleton = MockSingleton.new
 
    singleton_user = SingletonUser.new(singleton)
    
    singleton_user.do_something
    
    # assertions
  end
end
 
# 4. test
 
tester = SingletonTest.new
 
tester.test_singleton