From: "Hal E. Fulton" <hal9000@...>
Date: 2003-06-05T14:58:23+09:00
Subject: A unit testing problem...

Hello...

I'm trying to figure out how to test something 
properly and I'm seeking your input.

I'm talking to a device via a serial port. The
protocol is described in terms of hex, so for a
first pass I was using a sort of mock object
serial port stub:

  class SerialPort < IO

    attr_accessor :read_timeout, :sync

    def initialize(*args)
    end

    def putc(ch)
      STDOUT.printf "PC:    0x%02x\n", ch
    end

    def getc
      STDOUT.print "CM11A: "
      n = Integer(STDIN.gets)
      exit if n==999
      n
    end

  end

And I was pretending to be the receiving device and
talking back and forth to the PC in hex:

  C:\Windows\Desktop\projects\domo>ruby x10.rb
  CM11A: 0x5a
  PC:    0xc3
  PC:    0x2e
  PC:    0x66
  CM11A: 0x57
  PC:    0x2e
  PC:    0x66
  CM11A: 0x94
  PC:    0x00

But of course, interactive tests are not good in 
the long term.

How would you test this? For my first pass, I 
didn't have to make any changes to my X10 class;
I just substituted a fake SerialPort class.

I want to use StringIO, but it's not obvious to me
how to proceed.

I thought about sending fake arguments to the 
SerialPort constructor, which would then set up
StringIO objects... it was getting rather too
complex for my tastes. As I said, I don't want
to change the caller for the sake of testing.

What do you think?

Hal


--
Hal Fulton
hal9000@hypermetrics.com