class TestUser
  def is_ok?
    true
  end

  def receive_message
    yield("user", "message")
  end

  def &(other)
    test_user_group = TestUserGroup.new(self)
    test_user_group << other

    test_user_group
  end
end

class TestUserGroup
  attr_accessor :test_users

  def initialize(user)
    @test_users = [user]
  end

  def <<(other)
    (@test_users ||= []) << other
  end

  def &(other)
    <<(other)
  end

  def method_missing(method, *args, &block)
    result = []
    @test_users.each do |test_user|
      result << test_user.send(method, *args, &block)      
    end

    result
  end
end