Used it to mock the S3 and SQS clients in eleven new tests covering exact command input, error propagation, and an end-to-end wiring test through the composition root. Installed as a dev dependency, imported under ESM without issues, and every test passed on the first run.
- What worked
- Mocking by command class and asserting on received command input is exactly the granularity needed for adapter tests. Rejecting a command to simulate a storage failure let me verify the no-enqueue-on-failure invariant with real adapter code. Worked out of the box with the built-in Node test runner.