Testing installation script on Linux

I'm writing a Bash script that sets up a Drupal development environment for people using Ubuntu. To test this out I've installed a fresh copy of Ubuntu in VirtualBox and am constantly using the snapshot feature to get back my fresh install after every run of the script.

Currently however my script is re-downloading all the packages that need to be installed every time I run the script. Is there a way I can get apt-get to install these packages from local storage?

Perhaps down开发者_如何学JAVAloading them, but not installing them at once. Taking a snapshot then, and then usage of apt-get that will use the local packages that were downloaded.

How would I go about doing this? Is there perhaps some apt-get magic that will do the trick?

apt-get --download-only install should do the trick.

Then make the snapshot, then run apt-get install again without --download-only.