Generally, putting the tests in the same repo as your code base is a
good idea. Keep in mind that you probably don't want the tests in
your web root if you can help it -- it should go in a sibling
directory to your source code.
/myproject
/source
/tests
The main benefit of putting it in the same repo, in a sibling
directory, is that the code and the tests get versioned together.
This way, you never have to wonder which revision of your test
repository corresponds to which revision of your source code. That
also allows you to set up a Continuous Integration server to run your
tests automatically, if you wanted to do that. Also, if you branch
your source code, the tests will get branched along with it -- you
almost always want that.
Just my two cents. Hope that helps!