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JUnit is a regression testing framework written by Erich Gamma and Kent Beck. It is used by the developer who implements unit tests in Java.
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package org.junit.experimental.max;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Map;

import org.junit.runner.Description;
import org.junit.runner.Result;
import org.junit.runner.notification.Failure;
import org.junit.runner.notification.RunListener;

/**
 * Stores a subset of the history of each test:
 * 
 * Last failure timestamp
 * 
Duration of last execution
 * 
 */
public class MaxHistory implements Serializable {
    private static final long serialVersionUID = 1L;

    /**
     * Loads a {@link MaxHistory} from {@code file}, or generates a new one that
     * will be saved to {@code file}.
     */
    public static MaxHistory forFolder(File file) {
        if (file.exists()) {
            try {
                return readHistory(file);
            } catch (CouldNotReadCoreException e) {
                e.printStackTrace();
                file.delete();
            }
        }
        return new MaxHistory(file);
    }

    private static MaxHistory readHistory(File storedResults)
            throws CouldNotReadCoreException {
        try {
            FileInputStream file = new FileInputStream(storedResults);
            try {
                ObjectInputStream stream = new ObjectInputStream(file);
                try {
                    return (MaxHistory) stream.readObject();
                } finally {
                    stream.close();
                }
            } finally {
                file.close();
            }
        } catch (Exception e) {
            throw new CouldNotReadCoreException(e);
        }
    }

    private final Map fDurations = new HashMap();

    private final Map fFailureTimestamps = new HashMap();

    private final File fHistoryStore;

    private MaxHistory(File storedResults) {
        fHistoryStore = storedResults;
    }

    private void save() throws IOException {
        ObjectOutputStream stream = new ObjectOutputStream(new FileOutputStream(
                fHistoryStore));
        stream.writeObject(this);
        stream.close();
    }

    Long getFailureTimestamp(Description key) {
        return fFailureTimestamps.get(key.toString());
    }

    void putTestFailureTimestamp(Description key, long end) {
        fFailureTimestamps.put(key.toString(), end);
    }

    boolean isNewTest(Description key) {
        return !fDurations.containsKey(key.toString());
    }

    Long getTestDuration(Description key) {
        return fDurations.get(key.toString());
    }

    void putTestDuration(Description description, long duration) {
        fDurations.put(description.toString(), duration);
    }

    private final class RememberingListener extends RunListener {
        private long overallStart = System.currentTimeMillis();

        private Map starts = new HashMap();

        @Override
        public void testStarted(Description description) throws Exception {
            starts.put(description, System.nanoTime()); // Get most accurate
            // possible time
        }

        @Override
        public void testFinished(Description description) throws Exception {
            long end = System.nanoTime();
            long start = starts.get(description);
            putTestDuration(description, end - start);
        }

        @Override
        public void testFailure(Failure failure) throws Exception {
            putTestFailureTimestamp(failure.getDescription(), overallStart);
        }

        @Override
        public void testRunFinished(Result result) throws Exception {
            save();
        }
    }

    private class TestComparator implements Comparator {
        public int compare(Description o1, Description o2) {
            // Always prefer new tests
            if (isNewTest(o1)) {
                return -1;
            }
            if (isNewTest(o2)) {
                return 1;
            }
            // Then most recently failed first
            int result = getFailure(o2).compareTo(getFailure(o1));
            return result != 0 ? result
                    // Then shorter tests first
                    : getTestDuration(o1).compareTo(getTestDuration(o2));
        }

        private Long getFailure(Description key) {
            Long result = getFailureTimestamp(key);
            if (result == null) {
                return 0L; // 0 = "never failed (that I know about)"
            }
            return result;
        }
    }

    /**
     * @return a listener that will update this history based on the test
     *         results reported.
     */
    public RunListener listener() {
        return new RememberingListener();
    }

    /**
     * @return a comparator that ranks tests based on the JUnit Max sorting
     *         rules, as described in the {@link MaxCore} class comment.
     */
    public Comparator testComparator() {
        return new TestComparator();
    }
}