[Rd] Package tests: best practices

[hadley wickham]

I'm writing some tests for a package and I have a few questions
regarding best practices.  I've read "tests subdirectory" paragraph in
writing R extension, but I'm left wanting more.
Firstly, can I assume that the document root will always be set to the
test directory? (that what a couple of quick tests seemed to show)

Obviously, I want to test the code in my package - how do I load it? 
I assume I can't use library(XXX) because that will load the currently
installed version - should I source in all ../R/*.r instead?

Thanks for your advice,

Hadley