Explore the unique challenges and strategies for testing spacecraft software using pytest in this 30-minute PyCon US talk. Delve into the differences between testing web services and safety-critical systems, and learn how to assess verification needs based on software attributes and operational environments. Gain insights from real-world examples of spacecraft software testing at Varda Space Industries, showcasing pytest's powerful features like fixtures and hooks. Discover how to leverage Python language features such as generators, context managers, and threading to create effective tools for testing real-time telemetry streams and generating comprehensive test reports. From lessons learned from Ariane 5 and LightSail to implementing AutoHITL sequences and parametrized tests, acquire valuable knowledge to enhance your approach to testing mission-critical software systems.