I currently manage a rather large test suite (around 700 different tests) using Selenium, which is all written in Ruby and Rspec (although I've also used Cucumb

I currently manage a rather large test suite (around 700 different tests) using Selenium, which is all written in Ruby and Rspec (although I've also used Cucumber), and uses the gems Capybara (an abstraction layer for querying and manipulating the web browser via the Selenium driver) and SitePrism (for managing page objects and organizing re-usable sections). The entire suite runs in around 10 minutes on CircleCI, using 8 parallel threads (each running an instance of the Firefox Selenium driver), and it is rock solid stable. It took us a while to get to this point, though. The hard part is handling timing due to Javascript race conditions on the front-end. I had to write my own helper methods like "wait_for_ajax" that I sprinkle in various page object methods to wait for any jQuery AJAX requests to complete. I also use a "wait_until_true" method that can evaluate a block of code over and over until a time limit has been reached before throwing an exception. Once you figure out ways to solve those types of issues, testing things with Selenium becomes a lot more stable and easy. I have also used the exact same techniques (page objects, custom waiter methods for race conditions, etc) to test mobile apps on iOS and Android with Selenium. It can be a challenge, but once you have a system down and you know what you are doing, it's not so bad.