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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.runners.model;

import java.lang.annotation.Annotation;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.junit.Assert;
import org.junit.Before;
import org.junit.BeforeClass;

/**
 * Wraps a class to be run, providing method validation and annotation searching
 */
public class TestClass {
	private final Class fClass;

	private Map, List> fMethodsForAnnotations= new HashMap, List>();
	private Map, List> fFieldsForAnnotations= new HashMap, List>();

	/**
	 * Creates a {@code TestClass} wrapping {@code klass}. Each time this
	 * constructor executes, the class is scanned for annotations, which can be
	 * an expensive process (we hope in future JDK's it will not be.) Therefore,
	 * try to share instances of {@code TestClass} where possible.
	 */
	public TestClass(Class klass) {
		fClass= klass;
		if (klass != null && klass.getConstructors().length > 1)
			throw new IllegalArgumentException(
					"Test class can only have one constructor");

		for (Class eachClass : getSuperClasses(fClass)) {
			for (Method eachMethod : eachClass.getDeclaredMethods())
				addToAnnotationLists(new FrameworkMethod(eachMethod), fMethodsForAnnotations);
			for (Field eachField : eachClass.getDeclaredFields())
				addToAnnotationLists(new FrameworkField(eachField), fFieldsForAnnotations);
		}
	}

	private > void addToAnnotationLists(T member, Map, List> map) {
		for (Annotation each : member.getAnnotations()) {
			Class type= each.annotationType();
			List members= getAnnotatedMembers(map, type);
			if (member.isShadowedBy(members))
				return;
			if (runsTopToBottom(type))
				members.add(0, member);
			else
				members.add(member);
		}
	}

	/**
	 * Returns, efficiently, all the non-overridden methods in this class and
	 * its superclasses that are annotated with {@code annotationClass}.
	 */
	public List getAnnotatedMethods(
			Class annotationClass) {
		return getAnnotatedMembers(fMethodsForAnnotations, annotationClass);
	}

	/**
	 * Returns, efficiently, all the non-overridden fields in this class and
	 * its superclasses that are annotated with {@code annotationClass}.
	 */
	public List getAnnotatedFields(Class annotationClass) {
		return getAnnotatedMembers(fFieldsForAnnotations, annotationClass);
	}

	private  List getAnnotatedMembers(Map, List> map,
			Class type) {
		if (!map.containsKey(type))
			map.put(type, new ArrayList());
		return map.get(type);
	}

	private boolean runsTopToBottom(Class annotation) {
		return annotation.equals(Before.class)
				|| annotation.equals(BeforeClass.class);
	}

	private List> getSuperClasses(Class testClass) {
		ArrayList> results= new ArrayList>();
		Class current= testClass;
		while (current != null) {
			results.add(current);
			current= current.getSuperclass();
		}
		return results;
	}

	/**
	 * Returns the underlying Java class.
	 */
	public Class getJavaClass() {
		return fClass;
	}

	/**
	 * Returns the class's name.
	 */
	public String getName() {
		if (fClass == null)
			return "null";
		return fClass.getName();
	}

	/**
	 * Returns the only public constructor in the class, or throws an {@code
	 * AssertionError} if there are more or less than one.
	 */

	public Constructor getOnlyConstructor() {
		Constructor[] constructors= fClass.getConstructors();
		Assert.assertEquals(1, constructors.length);
		return constructors[0];
	}

	/**
	 * Returns the annotations on this class
	 */
	public Annotation[] getAnnotations() {
		if (fClass == null)
			return new Annotation[0];
		return fClass.getAnnotations();
	}
}