Note: I'm using the term feature in the sense of map feature, not in the sense of application feature or implemented requirement.
A simple pattern for such tests is
public class FeatureTest { @Test public void testAllFeatures() { for (Feature feature : findAllFeatures()) { testOneFeature(feature); } } private void testOneFeature(Feature feature) { // some logic with one or more JUnit assertions } }
Obviously, this naive approach has the following drawbacks:
- The test fails and terminates on the first incorrect feature. The remaining features will not be tested.
- All features get tested sequentially. This may take awfully long for a large database.
@RunWith(Parameterized.class) public class FeatureTest { // This is the parameter for each instance of the test. private Feature feature; public FeatureTest(Feature feature) { this.feature = feature; } @Parameters public static Collection<Object[]> getParameters() { List<Feature> features = findAllFeatures(); List<Object> parameters = new ArrayList<Object[]>(features.size()); for (Feature feature : features) { parameters.add(new Object[] { feature }; } return parameters; } @Test public void testOneFeature() { // assertions acting on the feature member } }
This solves the first problem: Each feature gets tested in its own test instance. Now if there is a large number of features or if each individual test is very expensive, we would like to run the test instances in parallel, using a thread pool, or maybe even a grid of multiple computers.
Browsing through the JUnit sources, I found a surprisingly easy way of parallelizing the tests with a thread pool, simply by using a custom runner:
@RunWith(Parallelized.class) public class FeatureTest { // same class body as above }
All you need is a simple extension of the Parameterized runner:
public class Parallelized extends Parameterized { private static class ThreadPoolScheduler implements RunnerScheduler { private ExecutorService executor; public ThreadPoolScheduler() { String threads = System.getProperty("junit.parallel.threads", "16"); int numThreads = Integer.parseInt(threads); executor = Executors.newFixedThreadPool(numThreads); } @Override public void finished() { executor.shutdown(); try { executor.awaitTermination(10, TimeUnit.MINUTES); } catch (InterruptedException exc) { throw new RuntimeException(exc); } } @Override public void schedule(Runnable childStatement) { executor.submit(childStatement); } } public Parallelized(Class klass) throws Throwable { super(klass); setScheduler(new ThreadPoolScheduler()); } }
The
RunnerScheduler
interface is fairly new in JUnit and marked as experimental. I discovered it in the current version JUnit 4.8.1 and found it missing in JUnit 4.4.0 which we have been using so far. RunnerScheduler
is also available in JUnit 4.7.0, but I did not check if this is the earliest version.
5 comments:
A very late thank you ! ;-)
Thanks! worked like a charm!
Thank you!
Great idea!
wow really nicely put
I somehow feel like I left a comment before...whatever, here's it (again).
The JUnit toolbox contains a really neat ParallelParameterized runner.
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