Get the slash prefixed path in Setup() is a good idea. I change the patch. I retain self.tempdir_name so we can use it in a test for no leading slash. The case creating index.html is OK with self.tempdir_name since we have changed our working directory to basetempdir.

I didn't think about compatibility but I know it's important. So rejecting the invalid request-targets is not a good idea to me now.