This blog post covers: why boundaries constitute the structure, why E2E/Integration tests are not enough, what does it even mean "Boundary/Contract tests", who should create such tests & why and how to match expectations of more than one consumer.P.S. All the contracts covered here are supposed to be internal. No multi-tenancy, no general-purpose APIs. Nada. Having a modular split within an application/system is absolutely crucial (beyond some scale), but ... like everything in this world, this comes with certain price to pay & challenges to tackle: boundary correctness - are boundaries set reasonable (to maximize the…