Throwaway dependencies

This tool starts the real dependencies a test needs (a database, a queue, an emulator of a cloud API) in containers for one test run, and removes them after it. The tests meet the real thing, and every run starts from the same clean state.

Finding it

How the project does it is found in the project. Look in the test dependencies for a container library that starts containers from the test code, and in the repository for a Compose file the tests use. CI shows how the project starts them and which container runtime it expects; the same runtime must be available wherever the tests run.

Using it

• Pin image versions: a fixed tag or digest, never latest, so a run today and a run next month test against the same dependency.
• Wait until ready: a health check, an open port or a log line, never a fixed sleep.
• Nothing shared between runs: a fresh container or a fresh database for each run, removed at the end (docker compose down -v removes the volumes too).
• Say when it could not start: without a container runtime the tests that need one did not run, and that is reported, not skipped in silence.

Examples: Testcontainers (several languages), Docker Compose, LocalStack (AWS services).