How do I write a unit test to verify async behavior using Spring 4 and annotations? - spring

Question

How do I write a unit test to verify async behavior using Spring 4 and annotations?
Since i'm used to Spring's (old) xml style), it took me some time to figure this out. So I thought I answer my own question to help others.

Answer 1

First the service that exposes an async download method:
#Service
public class DownloadService {
// note: placing this async method in its own dedicated bean was necessary
// to circumvent inner bean calls
#Async
public Future<String> startDownloading(final URL url) throws IOException {
return new AsyncResult<String>(getContentAsString(url));
}
private String getContentAsString(URL url) throws IOException {
try {
Thread.sleep(1000); // To demonstrate the effect of async
InputStream input = url.openStream();
return IOUtils.toString(input, StandardCharsets.UTF_8);
} catch (InterruptedException e) {
throw new IllegalStateException(e);
}
}
}
Next the test:
#RunWith(SpringJUnit4ClassRunner.class)
#ContextConfiguration
public class DownloadServiceTest {
#Configuration
#EnableAsync
static class Config {
#Bean
public DownloadService downloadService() {
return new DownloadService();
}
}
#Autowired
private DownloadService service;
#Test
public void testIndex() throws Exception {
final URL url = new URL("http://spring.io/blog/2013/01/16/next-stop-spring-framework-4-0");
Future<String> content = service.startDownloading(url);
assertThat(false, equalTo(content.isDone()));
final String str = content.get();
assertThat(true, equalTo(content.isDone()));
assertThat(str, JUnitMatchers.containsString("<html"));
}
}

Answer 2

If you are using the same example in Java 8 you could also use the CompletableFuture class as follows:
#Service
public class DownloadService {
#Async
public CompletableFuture<String> startDownloading(final URL url) throws IOException {
CompletableFuture<Boolean> future = new CompletableFuture<>();
Executors.newCachedThreadPool().submit(() -> {
getContentAsString(url);
future.complete(true);
return null;
});
return future;
}
private String getContentAsString(URL url) throws IOException {
try {
Thread.sleep(1000); // To demonstrate the effect of async
InputStream input = url.openStream();
return IOUtils.toString(input, StandardCharsets.UTF_8);
} catch (InterruptedException e) {
throw new IllegalStateException(e);
}
}
}
Now the test:
#RunWith(SpringJUnit4ClassRunner.class)
#ContextConfiguration
public class DownloadServiceTest {
#Configuration
#EnableAsync
static class Config {
#Bean
public DownloadService downloadService() {
return new DownloadService();
}
}
#Autowired
private DownloadService service;
#Test
public void testIndex() throws Exception {
final URL url = new URL("http://spring.io/blog/2013/01/16/next-stop-spring-framework-4-0");
CompletableFuture<Boolean> content = service.startDownloading(url);
content.thenRun(() -> {
assertThat(true, equalTo(content.isDone()));
assertThat(str, JUnitMatchers.containsString("<html"));
});
// wait for completion
content.get(10, TimeUnit.SECONDS);
}
}
Please that when the time-out is not specified, and anything goes wrong the test will go on "forever" until the CI or you shut it down.