如何检查ruby中是否定义了私有方法

我想要的是：

class Foo
  private

  def bar
    "bar"
  end

  magic_private_method_defined_test_method :bar #=> true
end

我尝试过的：

class Foo
  private

  def bar
    "bar"
  end

  respond_to? :bar #=> false
  #this actually calls respond_to on the class,and so respond_to :superclass gives true
  defined? :bar #=> nil
  instance_methods.include?(:bar) #=> false
  methods.include?(:bar) #=> false
  method_defined?(:bar) #=> false
  def bar
    "redefined!"
  end # redefining doesn't cause an error or anything

  public
  def bar
    "redefined publicly!"
  end #causes no error,behaves no differently whether or not #bar had been defined previously
end