Running this should only require Rails 2.2.2 or later, and the command line interfaces for sqlite3 and curl. Tested on Ubuntu Linux 9.04 (“Jaunty Jackalope”) and Mac OSX 10.5.6 (“Leopard”).

Installation of all necessary dependencies from a fresh install of Ubuntu 9.04:

sudo apt-get install rails git-core sqlite3 curl
sudo gem install rubygems-update
sudo /var/lib/gems/1.8/bin/update_rubygems
sudo gem install rails
sudo gem sources -a http://gems.github.com
sudo gem install rubys-gorp

Execution instructions:

This is a library which, among other things, will interpret ARGV.  Here's
an example based on http://github.com/rubys/awdwr:

ruby makedepot.rb [VERSION] [restore] [RANGE]... [save]

  "restore" - restore from snapshot before resuming execution

  "VERSION" specifies the Rails version to test.  Examples:
    edge
    _2.2.2_
    ~/git

  "RANGE" specifies a set of sections to execute.  Examples:
    6.2..6.5
    7.1-9.5
    16

  "save" - save snapshot after execution completes

Tests against the output produced (e.g., makedepot.html) can also be run separately:

ruby checkdepot.rb [partial]

"partial" means that tests which cover sections that are not included in
  makedepot.html are to be omitted.