java-testing-lab/spring-test-slices/README.md

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

./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)