Architecture

Repository model

src/main/java contains production kata implementations grouped by family (kyu3, kyu4, kyu5, kyu6, kyu7, leetcode, interview, coderun, other, transactions).
src/test/java mirrors the same package layout.
src/test/java/quality contains suite-level entry points for local and CI review:
- SmokeSuite – fast baseline visibility of all unit tests.
- IntegrationSuite – stateful transaction validation behavior.
- PropertySuite – jqwik property/invariant tests.
.github contains CI, templates, and dependency automation.

Deterministic API behavior where possible.
No mutable side effects in pure kata methods.
Input validation and boundary handling through explicit conditions.
Shared conventions and reviewability:
- test classes are colocated with implementation packages;
- critical branches are covered by regression-style tests where possible;
- build uses Maven with repeated quality checks in verify.

Static gates: Checkstyle, PMD, SpotBugs with zero-violation baselines enforced by Maven.
Coverage: JaCoCo with explicit thresholds on verify.
CI: split by JUnit tags (smoke, integration, property) plus full matrix verify.
Security: CodeQL workflow and Security policy in the repo root.
Intentional static-analysis exceptions: config/checkstyle/suppressions.xml documents generated smoke wrappers, while config/spotbugs-exclude.xml keeps Codewars-compatible public API names documented instead of hiding them in code.

Increase property coverage into additional stable, pure utilities where invariant checks are natural.
Add explicit domain-level integration tests for edge-case transaction flows (duplicates / ordering / insufficient balance).
Keep production methods with concise intent comments for non-obvious logic.