write-tests

name	write-tests
description	Use when adding or improving test coverage for KimPay - guides choosing the right test level and writing meaningful payment/concurrency/security tests.

Write Tests

Write tests that prove behavior and protect money-correctness. See .claude/rules/testing-strategy.md for the full strategy.

Choose the level

• Unit (default): pure logic with mocked collaborators (Mockito). Services, ledger math, crypto, signature/HMAC, masking. No Spring context.
• @DataJpaTest: repository query methods and mappings.
• @SpringBootTest + MockMvc: controller wiring, validation, security filters. Runs on H2 (PostgreSQL mode).
• Testcontainers: anything needing real Redis/Kafka/Postgres semantics.
• E2E: full secured flow with a real RSA keypair and signed request.

Write good tests

• One behavior per test; descriptive name (authenticateRejectsWrongSecret).
• Arrange clean state in @BeforeEach (delete in FK-safe order for integration tests).
• Assert with AssertJ on observable outcomes (status code, { code } envelope, persisted state) — not internal exception text.
• Enable security filters when testing auth; existing happy-path integration tests use addFilters = false.

Must-cover for payments

• Idempotency/concurrency: duplicate idempotency keys; parallel double-spend on one wallet; replayed nonce. Assert no overdraft / no double charge.
• Money math: partial refunds accumulate correctly and never exceed the remaining amount; ledger entries balance.
• Security: unauthenticated → 401; bad/replayed signature → 401; invalid input → 400; error bodies leak nothing.
• Failure paths: Redis/PSP down → graceful fallback, not an uncaught 500.

Anti-patterns

• Testing getters/framework code for coverage numbers.
• Asserting on log output or exact messages.
• One giant test that exercises ten behaviors.