Addressing the complexity of concurrency programming in the context of changing hardware remains an ongoing challenge. Overcoming limitations of conventional concurrency, I have investigated several ways of concurrency correctness verification in Scala. Initially, I investigated the transformation of software contracts into test-oracles to perform fully automated testing, a concept known from ongoing research in Eiffel. Therefore, I investigated several Design by Contracts tools and finally developed f-DBC, a novel tool based on a flexible component architecture for supporting functional Design by Contract in Scala. An performance analysis provides evidence that contracts written in f-DBC do not cause any measurable reduction in run-time performance compared to the same application without contracts. However, an empirical analysis of eight Eiffel and twelve Scala projects has provided evidence that contracts are seldom written in real world projects. Therefore, I have developed the main contribution of this book: a macro for the Scala compiler that replaces the initial approach with compiler checks on pure functions as these are the foundation of functional concurrency.