Spring Default API Vesrion Configuration in WebTestClient.ControllerSepc Not Applied

• Java 21
• Spring Boot 4.0 RC1
• Example Project: https://github.com/hantsy/spring7-sandbox/tree/master/boot-api-versioning-webflux

I tried to build a custom WebTestClient and run a test like this.

@WebFluxTest(controllers = GreetingController.class)
public class GreetingControllerTest {

    WebTestClient webTestClient;

    @Autowired GreetingController greetingController;

    @BeforeEach
    public void setup() {
        this.webTestClient = WebTestClient
                .bindToController(greetingController)
                .apiVersioning(apiVersionConfigurer ->
                        apiVersionConfigurer.useRequestHeader("X-API-Version")
                                .setDefaultVersion("1.0")
                )
                .configureClient()
                .apiVersionInserter(ApiVersionInserter.builder()
                        .useHeader("X-API-Version")
                        .build())
                .build();
    }

    @Test
    void testHello() {
        this.webTestClient.get().uri("/hello")
                // .apiVersion("1.0")
                .exchange()
                .expectBody(String.class).isEqualTo("Hello v1.0(Default)");
    }
}

It will fail the tests. It seems the setDefaultVersion in the following block is not applied.

  .apiVersioning(apiVersionConfigurer ->
          apiVersionConfigurer.useRequestHeader("X-API-Version")
                  .setDefaultVersion("1.0")
  )

But use a simple WebTestClientBuilderCustomizer to set the defaultApiVersion() on the Builder, it worked.

    @TestConfiguration
    static class TestConfig {

        @Bean
        WebTestClientBuilderCustomizer testClientBuilderCustomizer() {
            return builder -> builder.defaultApiVersion("1.0")
                    .apiVersionInserter(ApiVersionInserter.useHeader("X-API-Version"))
                    .build();
        }
    }

    @Autowired
    WebTestClient webTestClient;