Testing distributed systems, particularly durable workflows libraries, is inherently challenging due to the vast array of potential failures that can occur across processes and timings. Traditional unit and integration tests are insufficient for ensuring robustness at scale, necessitating more advanced strategies like formal verification, deterministic simulation testing, and chaos testing. Formal verification offers mathematical rigor but is difficult to implement due to the complexity of maintaining formal specifications and code. Deterministic simulation testing allows for controlled event ordering and fault injection but struggles with real-world dependency interactions. Chaos testing, favored for its ability to simulate realistic conditions, involves subjecting systems to random faults like server crashes and network issues to ensure they maintain critical properties such as workflow durability and queue reliability. This approach has proven effective in uncovering non-trivial bugs, such as race conditions triggered by precise database disconnection timings, which are hard to detect with conventional testing methods. The ultimate goal is to validate system-wide invariants, ensuring durable workflows remain reliable and easy to work with in real-world scenarios.