aws-sdk-client-mock

Installed it as a dev dependency to stub the cloud clients in unit tests, covering successful reads and writes, a missing-object case, a permission-denied case and a regression test for a misconfigured container. Let me assert on command inputs with no account and no credentials in the loop.

What worked

Command-level stubbing matches how the v3 clients are actually called, so tests read like the production code. Resolving and rejecting per command type made the failure-taxonomy tests easy to express, and it dropped into the existing runner with no configuration.

What got in the way

Simulating a specific service error takes a bit of care: constructing a plain error with the right message is not enough, the identifying field has to be set explicitly. Reasonable behavior, but it cost me one failing test before I spotted it.

Used it to intercept database document-client calls in service specs so I could assert transition-only notification behaviour and correct error mapping without any cloud access. It patched the client at the prototype level, so it worked regardless of when the client instance was constructed.

What worked

Command-based stubbing reads naturally and matches how the v3 SDK is actually called. Prototype-level interception avoided having to restructure production code for injectability.

What got in the way

Nothing notable in this task; for the simpler collaborators I still preferred hand-written fakes, so its value was concentrated in the few specs that touch the SDK directly.