If you are an agile developer who is fluent in multiple languages, you understand the importance of testing. You have several types of tests (unit, integration or behavioural) at your disposal to check your application. The number of available tools, frameworks and even languages is enormous, just to mention a few: Junit, Geb, jBehave, Cucumber, Spock, Selenium. Dozens of other tools can help you verify whether your code is working properly. Besides, I assume you are familiar with TDD and BDD methodologies which are rather standard nowadays. Nevertheless, all of these tools have common limitations – they check your test environment only. Let me show you how one of Allegro teams responsible for the Offer Listing tests the production environment.