Rakefile: The bare minimal you'll need to clone a test db from your env.

bare_bone_mysql_test.rake

require 'rubygems'
require 'rake'
require 'activerecord'

CURRENT_ENV = ENV['RAILS_ENV'] || 'development'
ROOT_PATH = File.dirname(__FILE__)
DB_CONFIG = YAML.load_file(File.join(ROOT_PATH, 'config', 'database.yml'))

namespace :db do
  namespace :structure do
    desc "Dump the database structure to a SQL file"
    task :dump do
      ActiveRecord::Base.establish_connection(DB_CONFIG[CURRENT_ENV])
      db_path = File.join(ROOT_PATH, 'db')
      mkdir db_path unless File.exists? db_path
      File.open(File.join(db_path, "#{CURRENT_ENV}_structure.sql"), 'w+') { |f| f << ActiveRecord::Base.connection.structure_dump }
    end
  end
  
  namespace :test do
    TEST_CONFIG = DB_CONFIG['test']
    
    desc "Create test database if it doesn't already exists"
    task :create do
      ActiveRecord::Base.establish_connection(TEST_CONFIG.merge('database'=>nil))
      ActiveRecord::Base.connection.create_database(TEST_CONFIG['database'], :charset => (TEST_CONFIG['charset'] || @charset), :collation => (TEST_CONFIG['collation'] || @collation))
      ActiveRecord::Base.establish_connection(TEST_CONFIG)
    end
    
    desc 'Empty the test database'
    task :purge do
      ActiveRecord::Base.establish_connection(TEST_CONFIG)
      ActiveRecord::Base.connection.recreate_database(TEST_CONFIG['database'], TEST_CONFIG)
    end


    desc "Recreate the test databases from the development structure"
    task :clone_structure => ['db:structure:dump', 'db:test:purge'] do
      ActiveRecord::Base.establish_connection(TEST_CONFIG)
      ActiveRecord::Base.connection.execute('SET foreign_key_checks = 0')
      IO.readlines("#{ROOT_PATH}/db/#{CURRENT_ENV}_structure.sql").join.split("\n\n").each do |table|
        ActiveRecord::Base.connection.execute(table)
      end
    end
  end
end