Building decoupled software is essential when you want to maintain velocity while developing a product in a global, distributed way. However, following the wrong parameters will handicap your quality assurance. How to be sure your product works? I’m a staunch advocate of using unit tests. They are faster and less flaky than integrated tests and allow you to scale up like a startup. Don’t be fooled! Integrated tests will kill your product. Among other things I will introduce the concept of contract testing and show you examples of PACT, the most suitable Java library to implement this concept.