Test if a Specific User Can Access a Location

Verify your assumptions about file permissions by testing them!

www-data comes to mind.  Will Apache be able to read that folder?

sudo -u <user> test -r </location/to/test>

sudo's -u allows you to specify a specific user (instead of the usual root).  Then run test -r which determines if the passed file exists and can be read.

NB. If your terminal isn't setup to display return codes then you can run the following (example with www-data):

sudo -u www-data test -r /var/data; echo $?

$? holds whatever the last command returned.  Generally, 0 => Success,  Not 0 => Failure.