CODEWITHSUNDEEP
javaspring-bootjunitmockitocompletable-future
rakesh
rakesh

Reputation: 304

Testing CompletableFuture.supplyAsync with Mockito

I am trying to test CompletableFuture.supplyAsync function with mockito but the test is not completing probably because the completable future is not returning. I am not sure what I am missing in the code. Can anyone please help.

I have written the code as follows. So there are UserService class which returns User, UserEntityService class which returns users entities and a validation class to check if the entities belongs to the user or not.

I want to test if the passed entities belongs to user or not.

class UserService {

    CompletableFuture<User> getUser(String userName) {
        log.info("Fetching User with username {}", userName);
        return CompletableFuture.supplyAsync(
                () -> getUserByPortalUserName(userName));
    }
}

class UserEntityService {

    CompletableFuture<List<UserEntity>> getUserEntities(Long userId) {
        log.info("Retrieving all entities for user id {}", userId);
        return CompletableFuture.supplyAsync(
                () -> getAllByUserId(userId));
    }
}

class UserValidationService {

    public boolean validateUserCounterparty(UserRequest request) 
                   throws ExecutionException, InterruptedException {
        CompletableFuture<Boolean> result = userService.getUser(request.getUserName())
                .thenCompose(user -> userEntityService.getUserEntities(user.getUserId()))
                .thenCompose(userEntities -> validate(userEntities, request.getUserEntities()));

        Boolean validationStatus = result.get();
        if (!validationStatus) {
            log.error("Validation failed for user name {}", request.getUserName());
        }
        return validationStatus;
    }
}

And the test case is written as

@ExtendWith(MockitoExtension.class)
class UserValidationServiceTest {

    @Mock
    UserService userService;

    @Mock
    UserEntityService userEntityService;

    @InjectMocks
    UserValidationService userValidationService;

    @Before
    public void init() {
        MockitoAnnotations.openMocks(this);
    }

    @Test
    public void validateUser() throws ExecutionException, InterruptedException {
        CompletableFuture<User> userFuture = new CompletableFuture<>();
        CompletableFuture<List<UserEntity>> userEntityFuture = new CompletableFuture<>();

        Mockito.doReturn(userFuture).when(userService).getUser(anyString());
        Mockito.doReturn(userEntityFuture).when(userEntityService).getUserEntities(anyLong());

        UserRequest request = UserRequest.builder()
                .userName("admin")
                .userEntities(List.of("US", "ASIA", "EUROPE")).build();


        boolean result = validationService.validateUserCounterparty(request);
        assertTrue(result);

    }
}

On executing this test, it goes into infinite loop and never stops. I guess its because the completable future is not returning but I dont have enough knowledge on how to prevent it.

What modification should I do to prevent it?

Upvotes: 3

Views: 14536

Answers (2)

thangdc94
thangdc94

Reputation: 1632

I faced the same issue today. @Jonasz's answer only works if you can mock the method in getUserEntities() and getUser(). But what if we have logics inside these methods and we still want unittest run through these methods.

My solution is to change behavior for CompletableFuture.supplyAsync() from async to sync by using static mock

mockStatic(CompletableFuture.class, invoca -> {
    if (invoca.getMethod().getName().equals("supplyAsync")) {
        Supplier<?> supplier = invoca.getArgument(0);
        return CompletableFuture.completedFuture(supplier.get());
    }
    return invoca.callRealMethod();
});

With this solution, I can run code inside async block and generic it for all CompletableFuture types

To use Static mock, you need to enable mock-inline. https://davidvlijmincx.com/posts/mockito_mock_static_method/

Upvotes: 1

Jonasz
Jonasz

Reputation: 1802

In your test method you're creating CompletableFuture instances using new. JavaDoc states:

public CompletableFuture()

Creates a new incomplete CompletableFuture.

So the objects you're creating are never completing, that's why the test is running infinitely. It's not actually a loop, but waiting on a blocking operation to be finished, which never happens.

What you need to do is define a CompletableFuture that completes - immediately or after some time. The simplest way of doing that is by using the static completedFuture() method:

CompletableFuture<User> userFuture =
        CompletableFuture.completedFuture(new User());
CompletableFuture<List<UserEntity>> userEntityFuture =
        CompletableFuture.completedFuture(List.of(new UserEntity()));

Thanks to that given objects are returned and the code can be executed fully. You can test errors in a similar way by using the failedFuture() method.

I've created a GitHub repo with a minimal reproducible example - the test presented there passes.

Upvotes: 4

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