# spring-test-slices

Companion code for the ankurm.com post *Spring Boot 4 Test Slices: @WebMvcTest, @JsonTest, @RestClientTest and @DataJpaTest Compared*.

A small book-catalogue app (controller, service, JPA repository, a `RestClient` client for an ISBN service, a Jackson 3
`@JacksonComponent`) and one test class per slice, plus the same app under a full `@SpringBootTest` as the baseline.
Every test writes the real output to `output/` and asserts the same facts, so the numbers in the post fail the build if
they stop being true.

| Tool | Version | Source |
|---|---|---|
| Spring Boot | 4.1.2 | `maven-metadata.xml` (latest GA when this was written; 4.2.0 is not GA yet) |
| Spring Framework | 7.0.10 | resolved by the Boot BOM |
| Hibernate ORM | 7.4.13.Final | resolved by the Boot BOM |
| JDK | 25 | |

## Run

```bash
./scripts/run-all.sh      # about a minute; regenerates everything in output/
mvn test                  # just the suite
```

Startup times (`output/30-startup-times.txt`) vary by machine and by run: treat them as indicative.

## Files

- `src/main/java/lab/slices/` the app: `BookController`, `ApiExceptionHandler`, `BookService`, `BookRepository`,
  `IsbnLookupClient`, `PriceJson` (`@JacksonComponent`), `AuditLogger` (a plain `@Component`, the canary)
- `src/test/java/lab/slices/` `WebMvcSliceTest`, `JsonSliceTest`, `RestClientSliceTest`, `DataJpaSliceTest`, `FullContextTest`,
  `PackageMovesTest`, `OldImportsCompileTest`, `FailureCaptureTest`, `ZMatrixTest`
- `src/test/java/lab/slices/failing/` test classes that fail on purpose (tag `failure-demo`, excluded from the normal run;
  `FailureCaptureTest` runs them through the JUnit Launcher and records the real exception)
- `src/broken/` Boot 3 style tests that no longer compile (not part of the Maven build; `OldImportsCompileTest` hands them to javac)
- `output/` captured real output of the last run

| Output | What it shows |
|---|---|
| `01` to `06` | one transcript per slice, plus the full context: requests, responses, and which beans exist |
| `07`, `08` | the exceptions a missing mock, a missing scan and `@EnableJpaAuditing` produce |
| `09` | where every test annotation lives in Boot 4.1.2, asked of the classpath |
| `10` | javac's own errors for Boot 3 imports |
| `20` | the bean-presence table, one column per slice |
| `11`, `12` | which Jackson each JSON tester wraps; which test jars `spring-boot-starter-test` alone brings in |
| `30` | context startup time per slice (indicative) |