I want to make sure that the Spring Boot WebFlux jUnit test passes through onErrorResume()

public class HealthCheckHandlerTest{

    private HealthCheckHandler;

    @Mock
    private repository repository;

    @Before
    public void setUp(){
        MockitoAnnotations.initMocks(this);
        // Generating a Test Instance
        handler = new HealthCheckHandler(repository);        
    }    

    @ Test
    Error in public void testHandleHealthMonitoring anomaly system 1_DB(){
        // preliminary preparation
        when(repository.hello()) .thenThrow(new RuntimeException("DB connection error"));

        // Running Tests
        Mono<ServerResponse>response=handler.handleHealthMonitoring (request);
        response.subscribe(r->r.statusCode());
    }
}

@Component
public class HealthCheckHandler {

    /**
     * repository
     */
    private final repository repository;

    /**
     * constructor
     *
     * @param repository
     */
    public HealthCheckHandler(
            Repository repository) {
        this.repository=repository;
    }

  /**
     * handler
     *
     * @param request
     * @return
     */
    public finalMono<ServerResponse>handleHealthMonitoring (finalServerRequest request) {
        // Try calling postgre for now to see if there are any errors.
        Mono<Map<String,Object>>postgreOpe=repository.hello();
        // Hogehoge is omitted this time.
        return Mono.zip (hogehoge, postgreOpe).flatMap(r->{
            return ServerResponse
                    .ok();
        }).timeout(Duration.ofSeconds(DURATION_TIME)) .onErrorResume(t->{
            logger.error("healthchecked for errors",t);
            return ServerResponse
                    .status(HttpStatus.INTERNAL_SERVER_ERROR)
                    .contentType(MediaType.APPLICATION_JSON)
                    .bodyValue("Error\n");
        });
    }
}