I worked on critical path backend services that processed credit card transactions at Paidy, a BNPL service used by companies like Apple and Amazon.

Due to the importance of reliability of the service, downtime wasn’t an option. As such, we wrote a large number of integration tests. However, as the test suite grew, running them locally took increasingly longer, which began to hurt the developer experience.

To solve this problem, I looked into migrating out tests to run on multiple threads, since they had been running single-threaded. By enabling parallel execution without modifying the tests themselves, we were able to significantly reduce the runtime, resulting in a much faster testing process.

In this talk, I’ll share the practical insights, and pitfalls of multithreaded testing in Rust. I’ll be covering how libraries like Wiremock are implemented, managing resource cleanup with Drop, and other methods using code examples.