/Users/ct/.rvm/gems/ruby-2.1.1/gems/headless-1.0.2/lib/headless/cli_util.rb:9:in ensure_application_exists!': Xvfb not found on your system (Headless::Exception)
from /Users/ct/.rvm/gems/ruby-2.1.1/gems/headless-1.0.2/lib/headless.rb:68:in initialize'
来自c_1319.rb：9：new'
from c_1319.rb:9:in'