package org.junit.rules;
import org.junit.runner.Description;
import org.junit.runners.model.Statement;
/**
* A TestRule is an alteration in how a test method, or set of test methods,
* is run and reported. A {@link TestRule} may add additional checks that cause
* a test that would otherwise fail to pass, or it may perform necessary setup or
* cleanup for tests, or it may observe test execution to report it elsewhere.
* {@link TestRule}s can do everything that could be done previously with
* methods annotated with {@link org.junit.Before},
* {@link org.junit.After}, {@link org.junit.BeforeClass}, or
* {@link org.junit.AfterClass}, but they are more powerful, and more easily
* shared
* between projects and classes.
*
* The default JUnit test runners for suites and
* individual test cases recognize {@link TestRule}s introduced in two different
* ways. {@link org.junit.Rule} annotates method-level
* {@link TestRule}s, and {@link org.junit.ClassRule}
* annotates class-level {@link TestRule}s. See Javadoc for those annotations
* for more information.
*
* Multiple {@link TestRule}s can be applied to a test or suite execution. The
* {@link Statement} that executes the method or suite is passed to each annotated
* {@link org.junit.Rule} in turn, and each may return a substitute or modified
* {@link Statement}, which is passed to the next {@link org.junit.Rule}, if any. For
* examples of how this can be useful, see these provided TestRules,
* or write your own:
*
* <ul>
* <li>{@link ErrorCollector}: collect multiple errors in one test method</li>
* <li>{@link ExpectedException}: make flexible assertions about thrown exceptions</li>
* <li>{@link ExternalResource}: start and stop a server, for example</li>
* <li>{@link TemporaryFolder}: create fresh files, and delete after test</li>
* <li>{@link TestName}: remember the test name for use during the method</li>
* <li>{@link TestWatcher}: add logic at events during method execution</li>
* <li>{@link Timeout}: cause test to fail after a set time</li>
* <li>{@link Verifier}: fail test if object state ends up incorrect</li>
* </ul>
*
* @since 4.9
*/
public interface TestRule {
/**
* Modifies the method-running {@link Statement} to implement this
* test-running rule.
*
* @param base The {@link Statement} to be modified
* @param description A {@link Description} of the test implemented in {@code base}
* @return a new statement, which may be the same as {@code base},
* a wrapper around {@code base}, or a completely new Statement.
*/
Statement apply(Statement base, Description description);
}