class Object
  def behaves_like?(object)
    expected_methods =
      if object.respond_to?(:instance_methods)
        object.instance_methods
      else
        object.methods
      end

    (expected_methods - methods).empty?
  end
end

class Foo
  def method1; end
end

class Bar
  def method1; end
  def method2; end
end

foo = Foo.new
bar = Bar.new

p foo.behaves_like?(Bar) # => false
p foo.behaves_like?(bar) # => false
p bar.behaves_like?(Foo) # => true
p bar.behaves_like?(foo) # => true