Testing/Specing rss feed generation validity?

I'm working on a rails site with an RSS feed. We were testing last
night, and I found that although Safari on my Mac was perfectly happy
with the feed, my colleagues Mac wasn't. So I ran it through the w3
validation site to work out the bugs.

So now, I'd like to incorporate rss feed validation into my bag of
Rails test/rspec tricks. Googling around I see that there's a plugin
to validate xhthl and css

And someone has munged this into an RSpec matcher to validate xhtml at least.

I thought that that code might form a base to talk to the X3 RSS feed
validator, but as I get into it it doesn't look that straightforward.

I was just wondering if anyone had trod this path before, or knew of
alternative plugins/gems to allow rss validation from a test or spec,
or at the very least from ruby.

You guys are too slow, I found the feedvalidator gem, which comes with
test:unit assertions, a few minutes later I had a working rspec