You can use a Virtual Machine to clone your production environment then play the migration.

This is my current configuration :

  Redmine version                3.0.0.stable
  Ruby version                   2.1.5-p273 (2014-11-13) [x86_64-linux]
  Rails version                  4.2.0
  Environment                    development
  Database adapter               Mysql2
  Subversion                     1.6.17
  Mercurial                      2.2.2
  Git                            1.9.1
  Xitolite                       1.9.1
Redmine plugins:
  redmine_bootstrap_kit          0.2.0
  redmine_git_hosting            1.0-devel
  redmine_sidekiq                2.1.0

Sudo version is 1.8.5p2 (but I don't think we should care of it now)
Debian Wheezy 7.8
Gitolite v3.6.2-12-g1c61d57

To install the devel branch

Follow the installation guide and when it comes to git checkout the branch for Redmine Git Hosting checkout the devel branch.

Then install development gems with :

redmine$ cd REDMINE_ROOT
redmine$ bundle install --without nothing

Play RSpec tests

## Copy the RSpec helper :
root$ su - redmine
redmine$ cd REDMINE_ROOT
redmine$ mkdir spec
redmine$ cp plugins/redmine_git_hosting/spec/root_spec_helper.rb spec/spec_helper.rb

## And watch the tests passing :)
redmine$ rspec plugins/redmine_git_hosting/spec/