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How can get my rake task to let Jenkins know that the build has failed?
rake test:browser

desc "Run browser tests."
task :browser => :environment do
    start = Time.now()
    puts "Stopping apache if running"
    system 'sudo apache2ctl stop'
    puts "Running selenium tests"
    Dir.glob('./test/browser/*.rb').each { |r|
        puts r
        system 'rvmsudo ruby ' +  r
    }
    system 'echo -e "a"'
    puts "All browser tests, elapsed: " + (Time.now() - start).to_s + " seconds"
end

system 'rvmsudo ruby ' +  r

sh 'rvmsudo ruby ' +  r do |ok, res|
     raise "Failed test." if !ok
 end