From: Frank Schmitt <invalid@...>
Date: 2004-03-18T22:24:32+09:00
Subject: Re: [help] unit testing when dealing with files

shasckaw <shasckaw@skynet.be> writes:

> Hello!
> I'm writting some code wich makes MD5 checksum on some files. I'd like
> to write a unit test for that code, but I don't know how to proceed. 

I'd use regression testing - compute the reference MD5 sum of your testfiles
using a known working MD5 implementation (e.g. md5 on Linux :-), and
check if your results are the same; sth like

#!/usr/bin/env ruby

require 'test/unit'

class MD5Test < Test::Unit::TestCase

  def test_empty_file
    # value computed by md5 for an empty file
    assert_equal("d41d8cd98f00b204e9800998ecf8427e",md5sum("empty_file"))
  end

end

Then, you just add additional testfiles until you're satisfied :-)
(BTW, I wouldn't use random files - when such a test fails, it can be
 hard to reproduce the failure, but YMMV).

> I have the same problem with another piece of code which launch a
> command line which generate some files. How can I unit test such
> things?

Hm. You could create some reference data files (validated by yourself), 
run your piece of code and just check for any differences between 
the reference files and the generated output - not very
elegant, but should work, e.g.

  def test_external_program
    call_external_program(outfile)
    assert(!system("diff #{outfile} #{referencefile} > /dev/null"))
  end
 
HTH & kind regards
frank

-- 
Frank Schmitt 
quattro research GmbH	
e-mail: schmitt NO at SPAM quattro-research !@! dot com