Spring Boot Testing Standards skill

Write unit, integration, and slice tests for Spring Boot 3 applications.

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Spring Boot Testing Standards

Priority: P0 (CRITICAL)

Core Rule Anchors

[BE-TEST-01] Parameterized Tests for Equivalent Cases: Prefer @ParameterizedTest (@CsvSource, @MethodSource) when methods have multiple equivalent inputs or boundary permutations. Distinct scenarios may stay separate test methods. Reviewers must not demand parameterized rewrites without a behavioral gap.
[BE-TEST-02] Ban on Brittle DB Mock String Matching: Do not use string-matching mocks for raw SQL queries. Test pure domain calculations directly, or use Testcontainers for database repository verification.
[BE-TEST-03] Ban on Shallow Assertions: Never assert only assertThat(result).isNotNull() without inspecting domain fields, status codes, and invariants.
[BE-TEST-04] Ban on Pass-Through Interface Mocks: Repositories and service handlers must test contract compliance and error mapping. Ban 1:1 pass-through mock echoing without contract assertions.
[BE-TEST-05] Bug-First Regression Lock: Every PR fixing a bug ticket or with title fix(...) must introduce a test reproducing the defect prior to the fix.

Follow TDD Workflow

Red: Write failing test (e.g., returns 404) ([BE-TEST-05]).
Green: Implement minimal code to pass.
Refactor: Clean up while keeping tests green ([BE-TEST-01]).
Coverage: Diagnostic and project-configured; verify risk-weighted critical paths rather than padding code for an arbitrary percentage.

Write Slice and Integration Tests

Real Infrastructure ([BE-TEST-02]): Use Testcontainers for DB/Queues. Avoid H2/Embedded.
Assertions ([BE-TEST-03]): Use AssertJ (assertThat) over JUnit assertions; avoid shallow checks.
Isolation ([BE-TEST-04]): Use @MockBean for downstream dependencies in Slice Tests; avoid pass-through mock echoing.

See implementation examples for WebMvcTest slice tests and Testcontainers integration tests.

Anti-Patterns

[BE-TEST-01] Stylistic parameterized rewrites: Do not demand parameterized refactoring of passing tests without a behavioral gap.
[BE-TEST-02] Brittle DB mock string matching: Do not match raw SQL strings in mocks; use Testcontainers.
[BE-TEST-03] Shallow assertions: Never assert only assertThat(result).isNotNull() without inspecting domain fields or status codes.
[BE-TEST-04] Pass-through mock echoing: Ban 1:1 pass-through mock echoing without contract assertions.
[BE-TEST-05] Bug fix without reproduction test: Ban bug fixes without a regression test.
No Dirty Contexts: Avoid @MockBean in base classes; it reloads context per test.
No network I/O in tests: Mock external calls with WireMock.
No System.out in tests: Use AssertJ assertions instead.

References

Implementation Examples

1	---
2	name: spring-boot-testing
3	description: Write unit, integration, and slice tests for Spring Boot 3 applications. Use when writing unit tests, integration tests, or slice tests for Spring Boot 3 applications.
4	metadata:
5	triggers:
6	files:
7	- '*/Test.java'
8	keywords:
9	- webmvctest
10	- datajpatest
11	- testcontainers
12	- assertj
13	---
14	# Spring Boot Testing Standards
15
16	## Priority: P0 (CRITICAL)
17
18	## Core Rule Anchors
19
20	- `[BE-TEST-01]` Parameterized Tests for Equivalent Cases: Prefer `@ParameterizedTest` (`@CsvSource`, `@MethodSource`) when methods have multiple equivalent inputs or boundary permutations. Distinct scenarios may stay separate test methods. Reviewers must not demand parameterized rewrites without a behavioral gap.
21	- `[BE-TEST-02]` Ban on Brittle DB Mock String Matching: Do not use string-matching mocks for raw SQL queries. Test pure domain calculations directly, or use `Testcontainers` for database repository verification.
22	- `[BE-TEST-03]` Ban on Shallow Assertions: Never assert only `assertThat(result).isNotNull()` without inspecting domain fields, status codes, and invariants.
23	- `[BE-TEST-04]` Ban on Pass-Through Interface Mocks: Repositories and service handlers must test contract compliance and error mapping. Ban 1:1 pass-through mock echoing without contract assertions.
24	- `[BE-TEST-05]` Bug-First Regression Lock: Every PR fixing a bug ticket or with title `fix(...)` must introduce a test reproducing the defect prior to the fix.
25
26	## Follow TDD Workflow
27
28	1. Red: Write failing test (e.g., `returns 404`) (`[BE-TEST-05]`).
29	2. Green: Implement minimal code to pass.
30	3. Refactor: Clean up while keeping tests green (`[BE-TEST-01]`).
31	4. Coverage: Diagnostic and project-configured; verify risk-weighted critical paths rather than padding code for an arbitrary percentage.
32
33	## Write Slice and Integration Tests
34
35	- Real Infrastructure (`[BE-TEST-02]`): Use Testcontainers for DB/Queues. Avoid H2/Embedded.
36	- Assertions (`[BE-TEST-03]`): Use AssertJ (`assertThat`) over JUnit assertions; avoid shallow checks.
37	- Isolation (`[BE-TEST-04]`): Use `@MockBean` for downstream dependencies in Slice Tests; avoid pass-through mock echoing.
38
39	See [implementation examples](references/implementation.md) for WebMvcTest slice tests and Testcontainers integration tests.
40
41	## Anti-Patterns
42
43	- `[BE-TEST-01]` Stylistic parameterized rewrites: Do not demand parameterized refactoring of passing tests without a behavioral gap.
44	- `[BE-TEST-02]` Brittle DB mock string matching: Do not match raw SQL strings in mocks; use Testcontainers.
45	- `[BE-TEST-03]` Shallow assertions: Never assert only `assertThat(result).isNotNull()` without inspecting domain fields or status codes.
46	- `[BE-TEST-04]` Pass-through mock echoing: Ban 1:1 pass-through mock echoing without contract assertions.
47	- `[BE-TEST-05]` Bug fix without reproduction test: Ban bug fixes without a regression test.
48	- No Dirty Contexts: Avoid @MockBean in base classes; it reloads context per test.
49	- No network I/O in tests: Mock external calls with WireMock.
50	- No System.out in tests: Use AssertJ assertions instead.
51	## References
52
53	- [Implementation Examples](references/implementation.md)