Spiffy capistrano config for composer based projects

deploy.rb

after "deploy", "deploy:cleanup"
after "deploy:update_code", "composer:install"
before "composer:install", "composer:copy_vendors"
after "composer:install", "phpunit:run_tests"

namespace :composer do
  desc "Copy vendors from previous release"
  task :copy_vendors, :except => { :no_release => true } do
    run "if [ -d #{previous_release}/vendor ]; then cp -a #{previous_release}/vendor #{latest_release}/vendor; fi"
  end
  task :install do
    run "sh -c 'cd #{latest_release} && curl -s http://getcomposer.org/installer | #{php_bin}'"
    run "sh -c 'cd #{release_path} && ./composer.phar install'"
  end
end

namespace :phpunit do
  desc "Test before making live"
  task :run_tests, :roles => :app do
    run "cd #{latest_release} && #{phpunit_bin}"
  end
end

You should add a composer.phar check if its available and add #{php_bin} before you call composer.phar

You might also want to check out roots/capistrano-composer.

@jeffbyrnes that works for cap 3 only. This snippet will work with cap 2.