Disable CSS Animations in Poltergeist & Phantomjs. Phantomjs does not like to wait for animations, and you can run in to nasty test flickers because of it. This pattern will disable animations in test env, and not touch any app code.

gistfile1.md

# env.rb or spec_helper.rb

Capybara.register_driver :poltergeist do |app|
  opts = {
    extensions: ["#{Rails.root}/features/support/phantomjs/disable_animations.js"] # or wherever
  }

  Capybara::Poltergeist::Driver.new(app, opts)
end

Capybara.javascript_driver = :poltergeist

// disable_animations.js
var disableAnimationStyles = '-webkit-transition: none !important;' +
                             '-moz-transition: none !important;' +
                             '-ms-transition: none !important;' +
                             '-o-transition: none !important;' +
                             'transition: none !important;'

window.onload = function() {
  var animationStyles = document.createElement('style');
  animationStyles.type = 'text/css';
  animationStyles.innerHTML = '* {' + disableAnimationStyles + '}';
  document.head.appendChild(animationStyles);
};

CJBridge's solution worked for us and seemed preferable over the middleware solution.