Howto develop PEAR package using data_dir

I'm developping my own PEAR package. I'm trying to keep as close to the PEAR standards as I can. I've got some data files with my package. During development these datafiles are in the same directory as my php files, but after installing the package with the pear command the files are in a different directory. I'm using PEAR_Config::singleton()->get('data_dir') to get the directory. Obviously testing the code fails because the files aren't in the data_dir, or maybe there are just old files there. But how do I easily run my code without installing the package over and over again?