From: Francis Hwang <sera@...>
Date: 2005-02-17T04:52:41+09:00
Subject: Re: [ANN] FileSystem 0.1.0: Beta for me, Alpha for you

On Feb 16, 2005, at 11:25 AM, Alexander Kellett wrote:

> does it already, or would it be possible, for this to act as an 
> overlay file system?
> as in, in a test, i can create a number of virtual files, any lookups 
> on real files
> succeed - thusly meaning that e.g loading of new libraries doesn't 
> screw up ;) - but
> any access to the virtual directories / files would return pseudo 
> objects.
>
> whats the feasibility of this? it would vastly simplify many testcases 
> i imagine.

Maybe this is what you're talking about:

At Rhizome, we send out lots of customized emails, with templates. So 
maybe you'll have a template file in 
/var/www/includes/email/welcome.tmpl . But if you want to play around 
with the codebase on, say, another server, this is annoying, because 
then you'd have to build up that directory path just to put one file in 
it.

So instead, I save a representative copy of that template somewhere in 
the test code directory, say test/test_data/email. Then, if we've got 
an email class that uses that template:

class WelcomeEmail < RhizMail::SimpleTemplateMessage
	def initialize( user )
		template = FileSystem.get_file.open( 
'/var/www/includes/email/welcome.tmpl' ) { |f| f.gets nil }
		super( template )
	end
end

the setup for the test code might look like this:

class TestWelcomeEmail < Test::Unit::TestCase
	def setup
		FileSystem.mock = true
		contents = File.open( 'test/test_data/email/welcome.tmpl' ) { |f|
			f.gets nil
		}
		FileSystem.mock_file_system.fill_path( '/var/www/includes/email' )
		FileSystem.get_file.open( '/var/www/includes/email/welcome.tmpl', 
File::CREAT | File::WRONLY ) { |f|
			f << contents
		}
	end
end

So that when the WelcomeEmail#initialize reads the contents of 
/var/www/includes/email/welcome.tmpl, it's actually reading contents 
from the virtual file system that was set up in your test case.

Is that what you had in mind?

Francis Hwang
http://fhwang.net/