Looking for browser emulator

[Roy Smith]

I've got to write some tests in python which simulate getting a page of 
HTML from an http server, finding a link, clicking on it, and then 
examining the HTML on the next page to make sure it has certain features.

I can use urllib to do the basic fetching, and lxml gives me the tools 
to find the link I want and extract its href attribute.  What's missing 
is dealing with turning the href into an absolute URL that I can give to 
urlopen().  Browsers implement all sorts of stateful logic such as "if 
the URL has no hostname, use the same hostname as the current page".  
I'm talking about something where I can execute this sequence of calls:

urlopen("http://foo.com:9999/bar")
urlopen("/baz")

and have the second one know that it needs to get 
"http://foo.com:9999/baz".  Does anything like that exist?

I'm really trying to stay away from Selenium and go strictly with 
something I can run under unittest.