def send_input(input)
      raise ArgumentError if input.nil? or input.try(:empty?)
      input.each_char { |char| @input.putc(char) }
    end
def send_input(input)
      raise ArgumentError if input.nil? or input.try(:empty?)
      input.each_char { |char| @input.putc(char) }
    end
Sends input to the slave process STDIN.

 Returns immediately.