Spring Boot @Async annotation and MockRestServiceServer

Question

I'm using Spring Boot 2.0.6 and Java 10. I did the following service that only hits an external rest api using RestTemplate.

@Service
@Slf4j
public class DbApiClientImpl implements DbApiClient {

  private final String URL_DELIMITER = "/";
  private RestTemplate restTemplate;
  private String url;

  public DbApiClientImpl(
      RestTemplateBuilder restTemplate,
      @Value("${dbapi.namespace}") String namespace,
      @Value("${dbapi.url}") String uri,
      @Value("${dbapi.username}") String username,
      @Value("${dbapi.password}") String password) {

  this.restTemplate = restTemplate.basicAuthorization(username, 
                      password).build();
  this.url = namespace.concat(uri);
}

   @Override
   @Async("asyncExecutor")
   public Merchant fetchMerchant(String id) {
       ResponseEntity<Merchant> response = 
        restTemplate.getForEntity(url.concat(URL_DELIMITER).concat(id), 
        Merchant.class);
   return response.getBody();
   }
}

And the following test using MockeRestServiceServer:

@RunWith(SpringRunner.class)
@RestClientTest(value = {DbApiClient.class})
public class DbApiClientTest {

   private static final String TEST_NAME = "test";
   private static final String TEST_NAME_BAD_REQUEST = "test- 
   1";
   private static final String TEST_NAME_SERVER_ERROR = 
  "test-2";

   @Autowired DbApiClient dbApiClient;

   @Value("${dbapi.namespace}")
   private String namespace;

   @Value("${dbapi.url}")
   private String dbApiUrl;

   @Autowired private MockRestServiceServer mockServer;

   @Autowired private ObjectMapper objectMapper;

   @Test
   public void test() throws 
   JsonProcessingException, IOException {
      Merchant mockMerchantSpec = populateFakeMerchant();
      String jsonResponse = 
          objectMapper.writeValueAsString(mockMerchantSpec);
      mockServer
         .expect(manyTimes(), 
           requestTo(dbApiUrl.concat("/").concat(TEST_NAME)))
         .andExpect(method(HttpMethod.GET))
         .andRespond(withSuccess(jsonResponse, 
                       MediaType.APPLICATION_JSON));

       assertNotNull(dbApiClient.fetchMerchant(TEST_NAME));
  }

The thing is that I'm getting the following exception when I run the test "No further request expected HTTP GET http://localthost... excecuted"

So seems that the @Async is borking MockerServerService response... Also, If I commented the @Async annotation everything works just fine and I get all test green.

Thanks in advance for your comments.

Update:

As per @M.Deinum's comment. I removed the CompletableFuture from the service but I'm still getting the same exception.

Answer 1

The problem is your code and not your test.

If you read the documentation (the JavaDoc) of AsyncExecutionInterceptor you will see the mention that only void or Future is supported as a return type. You are returning a plain object and that is internally treated as void.

A call to that method will always respond with null. As your test is running very quickly everything has been teared down already (or is in the process of being teared down) no more calls are expected to be made.

To fix, fix your method signature and return a Future<Merchant> so that you can block and wait for the result.

@Override
@Async("asyncExecutor")
public Future<Merchant> fetchMerchant(String id) {
   ResponseEntity<Merchant> response = 
    restTemplate.getForEntity(url.concat(URL_DELIMITER).concat(id), 
    Merchant.class);
   return CompletableFuture.completedFuture(response.getBody());
}

Now your calling code knows about the returned Future as well as the Spring Async code. Now in your test you can now call get on the returned value (maybe with a timeout to receive an error if something fails). TO inspect the result.