package org.codefx.demo.junit5; import org.junit.jupiter.api.extension.AfterTestExecutionCallback; import org.junit.jupiter.api.extension.ExtensionContext; import org.junit.jupiter.api.extension.ExtensionContext.Namespace; import org.junit.jupiter.api.extension.TestExecutionExceptionHandler; import org.opentest4j.AssertionFailedError; import java.util.Optional; import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation; public class ExpectedExceptionExtension implements TestExecutionExceptionHandler, AfterTestExecutionCallback { /* * This extension implements the exception handler callback to compare the thrown exception * to what was expected. The after test callback (which is called later) builds on * the results of that check and fails the test if an exception was expected but not thrown. */ private static final Namespace NAMESPACE = Namespace.create("org", "codefx", "ExpectedException"); private static final String KEY = "ExceptionWasT"; @Override public void handleTestExecutionException(ExtensionContext context, Throwable throwable) throws Throwable { boolean throwableMatchesExpectedException = expectedException(context) .filter(expected -> expected.isInstance(throwable)) .isPresent(); // in the `afterTestExecution` callback we have to pass or fail the test // depending on whether the exception was thrown or not; // to do that we need to register whether the exception was thrown; // (NOTE that if no exception was thrown, NOTHING is registered) if (throwableMatchesExpectedException) storeExceptionStatus(context, EXCEPTION.WAS_THROWN_AS_EXPECTED); else { // this extension is not in charge of the throwable, so we need to rethrow; storeExceptionStatus(context, EXCEPTION.WAS_THROWN_NOT_AS_EXPECTED); throw throwable; } } @Override public void afterTestExecution(ExtensionContext context) throws Exception { switch(loadExceptionStatus(context)) { case WAS_NOT_THROWN: expectedException(context) .map(expected -> new AssertionFailedError("Expected exception " + expected + " was not thrown.", expected, null)) .ifPresent(ex -> { throw ex; }); case WAS_THROWN_AS_EXPECTED: // the exception was thrown as expected so there is nothing to do case WAS_THROWN_NOT_AS_EXPECTED: // an exception was thrown but of the wrong type; // it was rethrown in `handleTestExecutionException` // so there is nothing to do here } } private static Optional<? extends Class<? extends Throwable>> expectedException(ExtensionContext context) { return context.getElement() .flatMap(el -> findAnnotation(el, Test.class)) .map(Test::expected) .filter(exceptionType -> exceptionType != Test.None.class); } private static void storeExceptionStatus(ExtensionContext context, EXCEPTION thrown) { context.getStore(NAMESPACE).put(KEY, thrown); } private static EXCEPTION loadExceptionStatus(ExtensionContext context) { EXCEPTION thrown = context.getStore(NAMESPACE).get(KEY, EXCEPTION.class); if (thrown == null) return EXCEPTION.WAS_NOT_THROWN; else return thrown; } private enum EXCEPTION { WAS_NOT_THROWN, WAS_THROWN_AS_EXPECTED, WAS_THROWN_NOT_AS_EXPECTED, } }