i have this url which is working:

which returns only the database missing elements of the input. i have a third party not modifiable service method like this:

public Mono<List<String>> getInvalidList(final Flux<String> input)

and to make this api work i’ve wrote this handler method:

public Mono<ServerResponse> getInvalidKeyItems(final ServerRequest req) {
    final EntryMessage message = log.traceEntry("getInvalidKeyItems[request={}]", req);

    return ServerResponse.ok().contentType(MediaType.APPLICATION_JSON)
            .body(service.getInvalidList(req.bodyToFlux(Integer.class).map(Object::toString)), List.class)
            .doOnSuccess(result -> log.traceExit(message, result));
}

and this router method:

    @Bean
    public RouterFunction<ServerResponse> getInvalidKeyItems(final KeyItemHandler handler) {
        return route(POST("/somePath").and(POST_AND_ACCEPT_JSON),
                handler::getInvalidKeyItems);
    }

which POST_AND_ACCEPT_JSON is a custom short variable for

RequestPredicates.method(HttpMethod.POST).and(RequestPredicates.accept(new MediaType[]{MediaType.APPLICATION_JSON}));

again, all of this is already working. what is not working is my router unit test:

@SpringBootTest
@ExtendWith({SpringExtension.class})
@AutoConfigureWebTestClient
class KeyItemRouterTest {

    @Autowired
    WebTestClient client;
    @MockBean
    KeyItemService service;

    @Test
    @WithMockUser
    void validateKeyItemTest() {
        Mockito.when(service.getInvalidList(Flux.fromIterable(List.of("1", "2", "3"))))
                .thenReturn(Mono.just(List.of("1")));

        client.post().uri("/somePath").contentType(MediaType.APPLICATION_JSON)
                .body(Mono.just(List.of("1", "2", "3")), List.class)

                .exchange()
                .expectStatus().isOk()

                .expectBody(List.class)
                .value(list -> Assertions.assertIterableEquals(List.of("2", "3"), list));
    }

which gets me this error:

{"timestamp":1714607064355,"path":"/somePath","status":"BAD_REQUEST","error":"'producer' must not be null","message":"'producer' must not be null","requestId":"46a88fc7","exception":"java.lang.IllegalArgumentException"}


java.lang.AssertionError: Status expected:<200 OK> but was:<400 BAD_REQUEST>
Expected :200 OK
Actual   :400 BAD_REQUEST

i’ve tried changing

.body(Mono.just(List.of("1", "2", "3")), List.class)

to

.bodyValue(List.of("1", "2", "3"))`

to

.body(BodyInserters.fromPublisher(Mono.just(List.of("1","2","3")), List.class))

but all of them resulted in the same error. how should i add a list of strings in my body request when unit testing?