As Voice AI applications evolve, developers face intricate challenges in testing, evaluating, and monitoring these systems, necessitating a comprehensive approach to ensure robust performance. This guide, based on insights from Brooke Hopkins of Coval and experiences from Langfuse users, emphasizes the importance of balancing online and offline evaluation strategies, which include real-time production monitoring and detailed component testing. It highlights the Voice AI Testing Pyramid, which is crucial for maintaining optimal performance, and distinguishes between single message evaluations and multi-turn conversation assessments. The development workflow is typically divided into early stages, focusing on quick integration and debugging, and later stages, which involve detailed performance monitoring and regression testing. Different types of voice applications, such as transactional and complex systems, require tailored evaluation focuses, whether it's individual function calls or conversation-level testing. Additionally, the integration of Coval with Langfuse offers users enhanced capabilities for end-to-end simulation testing, further enriching the evaluation process.