Rakefile

task :test, [:provider] => [:download_provider] do |t,args|
	puts "Now running test against provider '#{args[:provider]}'"
end

class DownloadTask < Rake::Task
  def needed?
    puts "\n#{self.class}.#{__callee__} - Don't know which file to check, " \
         "since I don't know which argument was passed to test task.\n\n"
    true
  end
end

def download(*args, &block)
  DownloadTask.define_task(*args, &block)
end

download 'download_provider', [:provider] do |t, args|
  puts "Now I know that the requested provider is '#{args[:provider]}'"
  puts "Downloading required image for provider '#{args[:provider]}'\n\n"
end