A lot has been said about how TDD (Test-Driven Development) is great for building up a developer’s confidence when changing code. However, TDD has its blind spots. By definition, you can't test with TDD what you don't develop, i.e. other systems you integrate with. In this talk, I'll demonstrate how despite of using TDD, a simple code change was the cause of failure in other systems. I'll explain why this happens and what you can do to minimize intersystem communication failure.