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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.util.ArrayList;
import java.util.Collections;
import java.util.List;

import junit.framework.TestSuite;

import org.junit.internal.requests.SortingRequest;
import org.junit.internal.runners.ErrorReportingRunner;
import org.junit.internal.runners.JUnit38ClassRunner;
import org.junit.runner.Description;
import org.junit.runner.JUnitCore;
import org.junit.runner.Request;
import org.junit.runner.Result;
import org.junit.runner.Runner;
import org.junit.runners.Suite;
import org.junit.runners.model.InitializationError;

/**
 * A replacement for JUnitCore, which keeps track of runtime and failure history, and reorders tests
 * to maximize the chances that a failing test occurs early in the test run.
 * 
 * The rules for sorting are:
 * 
 *  Never-run tests first, in arbitrary order
 * 
 Group remaining tests by the date at which they most recently failed.
 * 
 Sort groups such that the most recent failure date is first, and never-failing tests are at the end.
 * 
 Within a group, run the fastest tests first. 
 * 
 */
public class MaxCore {
	private static final String MALFORMED_JUNIT_3_TEST_CLASS_PREFIX= "malformed JUnit 3 test class: ";
	
	/**
	 * Create a new MaxCore from a serialized file stored at storedResults
	 * @deprecated use storedLocally()
	 */
	@Deprecated
	public static MaxCore forFolder(String folderName) {
		return storedLocally(new File(folderName));
	}
	
	/**
	 * Create a new MaxCore from a serialized file stored at storedResults
	 */
	public static MaxCore storedLocally(File storedResults) {
		return new MaxCore(storedResults);
	}

	private final MaxHistory fHistory;

	private MaxCore(File storedResults) {
		fHistory = MaxHistory.forFolder(storedResults);
	}

	/**
	 * Run all the tests in class.
	 * @return a {@link Result} describing the details of the test run and the failed tests.
	 */
	public Result run(Class testClass) {
		return run(Request.aClass(testClass));
	}

	/**
	 * Run all the tests contained in request.
	 * @param request the request describing tests
	 * @return a {@link Result} describing the details of the test run and the failed tests.
	 */
	public Result run(Request request) {
		return run(request, new JUnitCore());
	}

	/**
	 * Run all the tests contained in request.
	 * 
	 * This variant should be used if {@code core} has attached listeners that this
	 * run should notify.
	 * 
	 * @param request the request describing tests
	 * @param core a JUnitCore to delegate to.
	 * @return a {@link Result} describing the details of the test run and the failed tests.
	 */
	public Result run(Request request, JUnitCore core) {
		core.addListener(fHistory.listener());
		return core.run(sortRequest(request).getRunner());
	}
	
	/**
	 * @param request
	 * @return a new Request, which contains all of the same tests, but in a new order.
	 */
	public Request sortRequest(Request request) {
		if (request instanceof SortingRequest) // We'll pay big karma points for this
			return request;
		List leaves= findLeaves(request);
		Collections.sort(leaves, fHistory.testComparator());
		return constructLeafRequest(leaves);
	}

	private Request constructLeafRequest(List leaves) {
		final List runners = new ArrayList();
		for (Description each : leaves)
			runners.add(buildRunner(each));
		return new Request() {
			@Override
			public Runner getRunner() {
				try {
					return new Suite((Class)null, runners) {};
				} catch (InitializationError e) {
					return new ErrorReportingRunner(null, e);
				}
			}
		};
	}

	private Runner buildRunner(Description each) {
		if (each.toString().equals("TestSuite with 0 tests"))
			return Suite.emptySuite();
		if (each.toString().startsWith(MALFORMED_JUNIT_3_TEST_CLASS_PREFIX))
			// This is cheating, because it runs the whole class 
			// to get the warning for this method, but we can't do better, 
			// because JUnit 3.8's
			// thrown away which method the warning is for.
			return new JUnit38ClassRunner(new TestSuite(getMalformedTestClass(each)));
		Class type= each.getTestClass();
		if (type == null)
			throw new RuntimeException("Can't build a runner from description [" + each + "]");
		String methodName= each.getMethodName();
		if (methodName == null)
			return Request.aClass(type).getRunner();
		return Request.method(type, methodName).getRunner();
	}

	private Class getMalformedTestClass(Description each) {
		try {
			return Class.forName(each.toString().replace(MALFORMED_JUNIT_3_TEST_CLASS_PREFIX, ""));
		} catch (ClassNotFoundException e) {
			return null;
		}
	}

	/**
	 * @param request a request to run
	 * @return a list of method-level tests to run, sorted in the order
	 * specified in the class comment.
	 */
	public List sortedLeavesForTest(Request request) {
		return findLeaves(sortRequest(request));
	}
	
	private List findLeaves(Request request) {
		List results= new ArrayList();
		findLeaves(null, request.getRunner().getDescription(), results);
		return results;
	}
	
	private void findLeaves(Description parent, Description description, List results) {
		if (description.getChildren().isEmpty())
			if (description.toString().equals("warning(junit.framework.TestSuite$1)"))
				results.add(Description.createSuiteDescription(MALFORMED_JUNIT_3_TEST_CLASS_PREFIX + parent));
			else
				results.add(description);
		else
			for (Description each : description.getChildren())
				findLeaves(description, each, results);
	}
}