Verifying External Behavior

Most integration bugs are not coding errors. They are a belief about someone else's system — a status code, a parameter name, a response shape, a build backend's scoping rule — that was never checked and turned out to be wrong. The code is written correctly against a contract that does not exist.

The fix is not more care. It is a probe: a throwaway command that asks the real system the exact question, before the code is written. Probes cost seconds. The bugs they prevent are silent, ship green, and are found months later.

Probe the exact call you are about to write

Not a similar call, not the documented example — the same endpoint form, the same library version, the same argument spelling.

# A library's real defaults / return shapes, with no venv to create or clean up
uv run --no-project --with somelib python -c "import somelib; print(somelib.Thing())"