Testing, builds, and code quality

A reliable build produces the same reviewed artifact from the same source and toolchain.

Test layers

Unit tests: one behavior in memory, fast and focused.
Integration tests: real database, filesystem, network, or broker boundary.
Contract tests: producer and consumer agree on a protocol.
Property tests: invariants across many generated values.
Concurrency tests: coordinated races, timeouts, cancellation, and invariants.
End-to-end tests: a few critical deployed journeys.

Use JUnit 5 concepts such as lifecycle, parameterized tests, nested tests, assertions, and timeouts. Tests should be deterministic and independent.

Build tools

Maven and Gradle compile, test, package, resolve dependencies, and run plugins. Use the Maven/Gradle wrapper, Java toolchains, dependency locking or controlled resolution, reproducible archive settings, and CI verification.

Static quality

Compile with useful warnings. Apply formatting, static analysis, dependency vulnerability scanning, architecture rules, and coverage as evidence—not as substitutes for review.

Test design

Assert observable behavior. Avoid sleeping to coordinate concurrency. Use latches, barriers, fake clocks, and deterministic executors. Test boundaries: zero, negative, maximum, empty, null where allowed, overflow, DST, duplicate events, partial I/O, interruption, and malformed input.

Delivery

Package immutable JARs or runtime images. Record source revision, JDK, dependency graph, SBOM, checksums, and provenance. Deploy progressively and verify user health before promotion.

Feynman check

A unit test checks one gear. An integration test connects machines. A reproducible build is a factory that produces the same sealed parcel every time.