Summary

When using @TestInstance(PER_CLASS) with frameworks like Spring Boot, Quarkus, Micronaut, or others, non-static @MethodSource factory methods may call framework beans that depend on static @Container fields to produce arguments for parameterized tests. These factory methods run after postProcessTestInstance but before beforeEach, so containers must be started earlier than beforeAll.

With PER_CLASS, postProcessTestInstance is called exactly once (same as beforeAll), making it a suitable alternative for starting shared containers. This change moves shared container startup into postProcessTestInstance for PER_CLASS lifecycle, making them available during non-static @MethodSource resolution and for other TestInstancePostProcessor extensions.

Example

@TestInstance(TestInstance.Lifecycle.PER_CLASS)
@Testcontainers
@SpringBootTest
class UserServiceTest {

    @Container
    static PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:16");

    @Autowired
    UserService userService;

    // Non-static @MethodSource - requires PER_CLASS.
    // Calls a Spring bean that queries the database to produce test arguments.
    // Without this fix, postgres is not started yet when this method runs.
    Stream<Arguments> userArguments() {
        return userService.findAllRoles().stream()
            .map(Arguments::of);
    }

    @ParameterizedTest
    @MethodSource("userArguments")
    void should_create_user_with_role(String role) {
        // ...
    }
}