From the command line it's possible to run migrations in any environment. For example, using the code below it is possible to run migrations in the test environment.

rake db:migrate RAILS_ENV=test

Because the above code works it would appear that you could create the following rake task to automate running the migrations in the test environment.

task :test_migrate do
  ENV["RAILS_ENV"] = "test"
  Rake::Task["db:migrate"].invoke
end

Unfortunately, that didn't work, but the following change does work.

task :test_migrate do
  ActiveRecord::Base.establish_connection "test"
  Rake::Task["db:migrate"].invoke
end