1 package org.junit.rules; 2 3 import org.junit.runner.Description; 4 import org.junit.runners.model.Statement; 5 6 /** 7 * A TestRule is an alteration in how a test method, or set of test methods, 8 * is run and reported. A {@link TestRule} may add additional checks that cause 9 * a test that would otherwise fail to pass, or it may perform necessary setup or 10 * cleanup for tests, or it may observe test execution to report it elsewhere. 11 * {@link TestRule}s can do everything that could be done previously with 12 * methods annotated with {@link org.junit.Before}, 13 * {@link org.junit.After}, {@link org.junit.BeforeClass}, or 14 * {@link org.junit.AfterClass}, but they are more powerful, and more easily 15 * shared 16 * between projects and classes. 17 * 18 * The default JUnit test runners for suites and 19 * individual test cases recognize {@link TestRule}s introduced in two different 20 * ways. {@link org.junit.Rule} annotates method-level 21 * {@link TestRule}s, and {@link org.junit.ClassRule} 22 * annotates class-level {@link TestRule}s. See Javadoc for those annotations 23 * for more information. 24 * 25 * Multiple {@link TestRule}s can be applied to a test or suite execution. The 26 * {@link Statement} that executes the method or suite is passed to each annotated 27 * {@link org.junit.Rule} in turn, and each may return a substitute or modified 28 * {@link Statement}, which is passed to the next {@link org.junit.Rule}, if any. For 29 * examples of how this can be useful, see these provided TestRules, 30 * or write your own: 31 * 32 * <ul> 33 * <li>{@link ErrorCollector}: collect multiple errors in one test method</li> 34 * <li>{@link ExpectedException}: make flexible assertions about thrown exceptions</li> 35 * <li>{@link ExternalResource}: start and stop a server, for example</li> 36 * <li>{@link TemporaryFolder}: create fresh files, and delete after test</li> 37 * <li>{@link TestName}: remember the test name for use during the method</li> 38 * <li>{@link TestWatcher}: add logic at events during method execution</li> 39 * <li>{@link Timeout}: cause test to fail after a set time</li> 40 * <li>{@link Verifier}: fail test if object state ends up incorrect</li> 41 * </ul> 42 */ 43 public interface TestRule { 44 /** 45 * Modifies the method-running {@link Statement} to implement this 46 * test-running rule. 47 * 48 * @param base The {@link Statement} to be modified 49 * @param description A {@link Description} of the test implemented in {@code base} 50 * @return a new statement, which may be the same as {@code base}, 51 * a wrapper around {@code base}, or a completely new Statement. 52 */ apply(Statement base, Description description)53 Statement apply(Statement base, Description description); 54 } 55