Junit 4.11 cheatsheet

Assertion - org.junit.Assert

1. Equals, NotEquals, True, False, Null, NotNull - Arrays, Object & Strings

Test Aggregation

import org.junit.runner.RunWith;
import org.junit.runners.Suite;

@RunWith(Suite.class)
@Suite.SuiteClasses({
  TestFeatureLogin.class,
  TestFeatureLogout.class,
  TestFeatureNavigate.class,
  TestFeatureUpdate.class
})

public class FeatureTestSuite {
  // the class remains empty,
  // used only as a holder for the above annotations
}

Exception Testing

  @Test(expected= IndexOutOfBoundsException.class) 
  public void empty() { 
       new ArrayList<Object>().get(0); 
  }

    @Rule
    public ExpectedException thrown = ExpectedException.none();

    @Test
    public void shouldTestExceptionMessage() throws IndexOutOfBoundsException {
        List

Matchers and assertthat

assertThat(x, is(3));
assertThat(x, is(not(4)));
assertThat(responseString, either(containsString("color")).or(containsString("colour")));
assertThat(myList, hasItem("3"));

Ignoring tests

@Ignore("Test is ignored as a demonstration")
@Test
public void testSane() {
    assertThat(1, is(1));
}

Timeout for tests

@Test(timeout=1000)
public void testWithTimeout() {
  ...
}

public class HasGlobalTimeout {
    public static String log;

    @Rule
    public Timeout globalTimeout = new Timeout(10000); // 10 seconds max per method tested

    @Test
    public void testInfiniteLoop1() {
        log += "ran1";
        for (;;) {
        }
    }

    @Test
    public void testInfiniteLoop2() {
        log += "ran2";
        for (;;) {
        }
    }
}

Multithreaded code and concurrency

Java code can be difficult to test for thread safety when multithreading.

The article at http://www.planetgeek.ch/2009/08/25/how-to-find-a-concurrency-bug-with-java/ describes a method of exposing concurrency bugs that adds a new assertion method assertConcurrent.

To use this you pass in a Collection of Runnables that are your arrange\act\assert test on the SUT, they all run at the same time in theassertConcurrent method; the chances of triggering a multithreading code error, and thereby failing some assertion are greatly increased:

The assertConcurrent method from the article is:

 public static void assertConcurrent(final String message, final List extends Runnable> runnables, final int maxTimeoutSeconds) throws InterruptedException {
   final int numThreads = runnables.size();
   final List<Throwable> exceptions = Collections.synchronizedList(new ArrayList<Throwable>());
   final ExecutorService threadPool = Executors.newFixedThreadPool(numThreads);
   try {
  final CountDownLatch allExecutorThreadsReady = new CountDownLatch(numThreads);
  final CountDownLatch afterInitBlocker = new CountDownLatch(1);
  final CountDownLatch allDone = new CountDownLatch(numThreads);
  for (final Runnable submittedTestRunnable : runnables) {
    threadPool.submit(new Runnable() {
   public void run() {
     allExecutorThreadsReady.countDown();
     try {
    afterInitBlocker.await();
    submittedTestRunnable.run();
     } catch (final Throwable e) {
    exceptions.add(e);
     } finally {
    allDone.countDown();
     }
   }
    });
  }
  // wait until all threads are ready
  assertTrue("Timeout initializing threads! Perform long lasting initializations before passing runnables to assertConcurrent", allExecutorThreadsReady.await(runnables.size() * 10, TimeUnit.MILLISECONDS));
  // start all test runners
  afterInitBlocker.countDown();
  assertTrue(message +" timeout! More than" + maxTimeoutSeconds + "seconds", allDone.await(maxTimeoutSeconds, TimeUnit.SECONDS));
   } finally {
  threadPool.shutdownNow();
   }
   assertTrue(message + "failed with exception(s)" + exceptions, exceptions.isEmpty());
 }

Another article giving an overview of alternative stragies at http://tempusfugitlibrary.org/recipes/2012/05/20/testing-concurrent-code/ might also be useful.

Java Concurrency Bookshelf

• The Java Memory Model and Thread Specification JSR-133
• Threads and Locks, Java Virtual Machine Specification
• The book Java Concurrency in Practice by Brian Goetz (Amazon UK).
• Double Checked Locking article by Doug Lea
• Doug Lea's homepage