The document discusses testing asynchronous code using various techniques and frameworks like JUnit and Mocha for handling event-driven architectures, including performance considerations. It covers methods for calculating Fibonacci numbers, implementing a polling mechanism, and ensuring thread safety during tests. Key takeaways emphasize the importance of synchronization methods and validating them through unit tests, with references to relevant literature on concurrency.

1. Asynchronen
Code testen
@ndrssmn
Andreas Simon

2. Synchron
Übertragungszeit
Wartezeit
Bearbeitungszeit
Wartezeit
Antwortzeit

3. Asynchron
Antwortzeit
Wartezeit

4. Fehlertoleranz
Verfügbarkeit
Parallelisierung
Performance
Event-Driven Architecture

5. Listening
Callback

7. Synchronisation
TIMEOUT

8. Listening in JUnit
@Test public void
should_reply_with_Fibonacci_numbers() throws Exception {
// Arrange
NotificationTrace<Integer> trace = new NotificationTrace<>(TIMEOUT);
String replyQueue = channel.queueDeclare().getQueue();
FibonacciCalculator.create(connection.createChannel());
new IntegerConsumer(
connection.createChannel(),
trace::append)
.consumeQueue(replyQueue);
// Act
publishNumbers(MIN, MAX, replyQueue);
// Assert
trace.containsNotification(equalTo(FIB_MIN));
trace.containsNotification(equalTo(FIB_MAX));
}

9. Listening in Mocha
describe('AMQP Fibonacci service', function() {
it('calculates fib(' + MIN + ')', function(done) {
connection.on('ready', function () {
connection.queue('my-queue', function(q) {
q.subscribe(function (message) {
try {
// Assert
message.data.toString().should.eql(FIB_MIN);
done();
} catch(e) {
done(e);
}
});
// Act
connection.publish(
'calculate-fibonacci', MIN,
{ replyTo: 'my-queue'}
);
});
});
});

10. Sampling
POST localhost/
CREATED Location: localhost/30
GET localhost/30
NOT FOUND
GET localhost/30
NOT FOUND
GET localhost/30
OK :: 832040
TIMEOUT

11. Sampling in JUnit
@Test public void
calculates_fib_30() throws Exception {
// Act
connection = POST("http://localhost:3000/", "30");
fibLocation = connection.getHeaderField("Location");
// Assert
Probe probe = responseTo(
fibLocation,
equalTo(Integer.toString(FIB_30))
);
new Poller(TIMEOUT, POLL_DELAY).check(probe);
}

12. public class Poller {
[…]
public void check(Probe probe) {
[…]
while (!probe.isSatisfied()) {
[…]
Thread.sleep(pollDelayMillis);
probe.sample();
}
}
}
public interface Probe {
void sample();
boolean isSatisfied();
void describeAcceptanceCriteriaTo(Description d);
void describeFailureTo(Description d);
}

13. Sampling in Mocha
describe('Fibonacci server', function() {
it('should calculate fib(20)', function(done) {
var req = http.request(POST_fib, function(res) {
res.setEncoding('utf8');
res.statusCode.should.eql(201);
res.headers.location.should.be.ok;
pollGET(res.headers.location, done);
}).on('error', done);
req.setHeader('Content-Type', 'application/x-www-form-
urlencoded;charset=UTF-8');
req.write('n=20n');
req.end();
});

14. Sampling in Mocha
function pollGET(url, done) {
http.get(url, function(res) {
if(200 != res.statusCode) {
setTimeout(pollGET, POLL_DELAY, url, done);
}
res.on('data', function (chunk) {
chunk.toString().should.eql('6765');
done();
});
}).on('error', done);
}

15. Test the test
@Test public void
is_thread_safe() throws Exception {
latch = startStressing(STRESSING_THREADS, () -> {
for (int i = 0; i < ITERATIONS; i++) {
trace.append("NOT-WANTED");
Thread.sleep(SLEEPTIME);
}
latch.countDown();
});
scheduler.schedule(
() -> trace.append("WANTED"),
100, TimeUnit.MILLISECONDS
);
trace.containsNotification(equalTo("WANTED"));
latch.await();
assertThat(
trace.getAppendCount(),
is(equalTo((long) STRESSING_THREADS * ITERATIONS + 1))
);
}

16. Thread-sicher implementieren
public class NotificationTrace<T> {
public void append(T message) {
synchronized (traceLock) {
trace.add(message);
traceLock.notifyAll();
}
}
public void containsNotification(Matcher<? super T> criteria)
throws AssertionError, InterruptedException {
Timeout timeout = new Timeout(timeoutMs);
synchronized (traceLock) {
stream = new NotificationStream<>(trace, criteria);
while (!stream.hasMatched()) {
if (timeout.hasTimedOut()) {
throw new AssertionError();
}
timeout.waitOn(traceLock);
}
}
}

17. Aufräumen
@After
public void tearDown() throws InterruptedException {
executorService.shutdownNow();
scheduler.shutdownNow();
}

18. Fazit
Listening vs. Sampling
Synchronisierungsmechanismen kapseln (und durch Unit-Tests
validieren)
Brian Goetz: "Java Concurrency in Practice"
Nat Pryce, Steve Freeman: "Growing Object-Oriented Software"
https://github.com/andreassimon/talk-asynchronen-code-testen

19. Quagilis
Andreas Simon
Lazarettstr. 9
48147 Münster
Fon +49 (0) 251 - 590 491 55-0
Fax +49 (0) 251 - 590 491 55-9
a.simon@quagilis.de
http://www.quagilis.de
Quality in Agile.