entering an already defined directory fails

I created /var/tmp/testing, chowned it to northscale, then tried to use it for my db directory. I received a validation message "Cannot configure resources due to:
Could not set the storage path. It must be a new directory and the 'northscale' user must have permissions to create it."

I suspect the mkdir attempt failed because it already exists. This may be done by root in some other place, so this kind of thing should be allowed.