jars/junit5-r5.10.2/documentation/src/test/java/example/extensions/RandomNumberExtension.java

/*
 * Copyright 2015-2023 the original author or authors.
 *
 * All rights reserved. This program and the accompanying materials are
 * made available under the terms of the Eclipse Public License v2.0 which
 * accompanies this distribution and is available at
 *
 * https://www.eclipse.org/legal/epl-v20.html
 */

package example.extensions;

// tag::user_guide[]

import static org.junit.platform.commons.support.AnnotationSupport.findAnnotatedFields;

import java.lang.reflect.Field;
import java.util.function.Predicate;

import org.junit.jupiter.api.extension.BeforeAllCallback;
import org.junit.jupiter.api.extension.BeforeEachCallback;
import org.junit.jupiter.api.extension.ExtensionContext;
import org.junit.jupiter.api.extension.ParameterContext;
import org.junit.jupiter.api.extension.ParameterResolver;
import org.junit.platform.commons.support.ModifierSupport;

// end::user_guide[]
// @formatter:off
// tag::user_guide[]
class RandomNumberExtension
		implements BeforeAllCallback, BeforeEachCallback, ParameterResolver {

	private final java.util.Random random = new java.util.Random(System.nanoTime());

	/**
	 * Inject a random integer into static fields that are annotated with
	 * {@code @Random} and can be assigned an integer value.
	 */
	@Override
	public void beforeAll(ExtensionContext context) {
		Class<?> testClass = context.getRequiredTestClass();
		injectFields(testClass, null, ModifierSupport::isStatic);
	}

	/**
	 * Inject a random integer into non-static fields that are annotated with
	 * {@code @Random} and can be assigned an integer value.
	 */
	@Override
	public void beforeEach(ExtensionContext context) {
		Class<?> testClass = context.getRequiredTestClass();
		Object testInstance = context.getRequiredTestInstance();
		injectFields(testClass, testInstance, ModifierSupport::isNotStatic);
	}

	/**
	 * Determine if the parameter is annotated with {@code @Random} and can be
	 * assigned an integer value.
	 */
	@Override
	public boolean supportsParameter(ParameterContext pc, ExtensionContext ec) {
		return pc.isAnnotated(Random.class) && isInteger(pc.getParameter().getType());
	}

	/**
	 * Resolve a random integer.
	 */
	@Override
	public Integer resolveParameter(ParameterContext pc, ExtensionContext ec) {
		return this.random.nextInt();
	}

	private void injectFields(Class<?> testClass, Object testInstance,
			Predicate<Field> predicate) {

		predicate = predicate.and(field -> isInteger(field.getType()));
		findAnnotatedFields(testClass, Random.class, predicate)
			.forEach(field -> {
				try {
					field.setAccessible(true);
					field.set(testInstance, this.random.nextInt());
				}
				catch (Exception ex) {
					throw new RuntimeException(ex);
				}
			});
	}

	private static boolean isInteger(Class<?> type) {
		return type == Integer.class || type == int.class;
	}

}
// end::user_guide[]
// @formatter:on