How to invoke Test.hello() from class Alpha/Beta?

hello.rb

 module Hello

  class Test 
    attr_accessor :registers

    def initialize()
      @registers = []

      @registers << Alpha.new
      @registers << Beta.new
    end

    def display
      p @registers
    end

    def hello()
      p "Hello"
    end
  end

  class Alpha
    def initialize()
      @registers = "Alpha"
      # How to call Test.hello() from here?
    end
  end

  class Beta
    def initialize()
      @registers = "Beta"
    end
  end
end

h = Hello::Test.new()
h.display()