Retry JUnit failed tests immediately

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Post summary: How to retry failed JUnit tests immediately and if retry is OK report test as passed.

Approaches

There are mainly three approaches to make JUnit retry failed tests.

  • Maven Surefire or Failsafe plugins – follow plugin name links for more details how to use and configure plugins
  • JUnit rules – code listed in current post can be used as a rule. See more for rules in Use JUnit rules to debug failed API tests post. Problem is @Rule annotation works for test methods only. In order to have retry logic in @BeforeClass then @ClassRule object should be instantiated.
  • JUnit custom runner – this post is dedicated on creating own JUnit retry runner and run tests with it.

Custom JUnit retry runner

Custom runner can be created by extending org.junit.runners.BlockJUnit4ClassRunner class and override public void run(final RunNotifier notifier) and protected void runChild(final FrameworkMethod method, RunNotifier notifier) methods. run() is accessed when test class is instantiated, runChild() is accessed when test method is run. Bellow is the code for custom JUnit retry runner class:

package com.automationrhapsody.junit.runners;

import org.junit.Ignore;
import org.junit.internal.AssumptionViolatedException;
import org.junit.internal.runners.model.EachTestNotifier;
import org.junit.runner.Description;
import org.junit.runner.notification.RunNotifier;
import org.junit.runner.notification.StoppedByUserException;
import org.junit.runners.BlockJUnit4ClassRunner;
import org.junit.runners.model.FrameworkMethod;
import org.junit.runners.model.InitializationError;
import org.junit.runners.model.Statement;

public class RetryRunner extends BlockJUnit4ClassRunner {

	private static final int RETRY_COUNT = 2;

	public RetryRunner(Class<?> clazz) throws InitializationError {
		super(clazz);
	}

	@Override
	public void run(final RunNotifier notifier) {
		EachTestNotifier testNotifier = new EachTestNotifier(notifier, getDescription());
		Statement statement = classBlock(notifier);
		try {
			statement.evaluate();
		} catch (AssumptionViolatedException ave) {
			testNotifier.fireTestIgnored();
		} catch (StoppedByUserException sbue) {
			throw sbue;
		} catch (Throwable t) {
			System.out.println("Retry class: " + getDescription().getDisplayName());
			retry(testNotifier, statement, t, getDescription());
		}
	}

	@Override
	protected void runChild(final FrameworkMethod method, RunNotifier notifier) {
		Description description = describeChild(method);
		if (method.getAnnotation(Ignore.class) != null) {
			notifier.fireTestIgnored(description);
		} else {
			runTest(methodBlock(method), description, notifier);
		}
	}

	private void runTest(Statement statement, Description description, RunNotifier notifier) {
		EachTestNotifier eachNotifier = new EachTestNotifier(notifier, description);
		eachNotifier.fireTestStarted();
		try {
			statement.evaluate();
		} catch (AssumptionViolatedException e) {
			eachNotifier.addFailedAssumption(e);
		} catch (Throwable e) {
			System.out.println("Retry test: " + description.getDisplayName());
			retry(eachNotifier, statement, e, description);
		} finally {
			eachNotifier.fireTestFinished();
		}
	}

	private void retry(EachTestNotifier notifier, Statement statement, Throwable currentThrowable, Description info) {
		int failedAttempts = 0;
		Throwable caughtThrowable = currentThrowable;
		while (RETRY_COUNT > failedAttempts) {
			try {
				System.out.println("Retry attempt " + (failedAttempts + 1) + " for " + info.getDisplayName());
				statement.evaluate();
				return;
			} catch (Throwable t) {
				failedAttempts++;
				caughtThrowable = t;
			}
		}
		notifier.addFailure(caughtThrowable);
	}
}

Code shown above is available in GitHub java-samples/junit repository.

Using JUnit RetryRunner

In order to configure JUnit test to use the runner, class holding tests should be annotated with @RunWith:

@RunWith(RetryRunner.class)
public class RetryRunnerTests {
	@Test
	public void testRetrySuccessFirstTime() {
		assertTrue(true);
	}
}

Conclusion

Making JUnit to rerun is easy, the harder thing to do is to fix your tests so they pass from first time. Generally it is not a good to have tests that are flaky.

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