我知道可以在 JUnit 中定义 'expected' 异常，这样做：
@Test(expect=MyException.class)
public void someMethod() { ... }
但是，如果总是抛出相同的异常，但使用不同的“嵌套”呢？ 原因。
有什么建议吗？
【问题讨论】：
从 JUnit 4.11 开始，您可以使用 ExpectedException 规则的 expectCause() 方法：
import static org.hamcrest.CoreMatchers.*;
// ...
@Rule
public ExpectedException expectedException = ExpectedException.none();
@Test
public void throwsNestedException() throws Exception {
expectedException.expectCause(isA(SomeNestedException.class));
throw new ParentException("foo", new SomeNestedException("bar"));
}
【讨论】：
expectedException.expectCause(is(IsInstanceOf.<Throwable>instanceOf(SomeNestedException.class))); 但除此之外，这是一个优雅的解决方案。
expectedException.expectCause(IsInstanceOf.<Throwable>instanceOf(SomeNestedException.class));
isA 作为 is(instanceOf(clazz)) 的简写，所以这就足够了：expectedException.expectCause(isA(SomeNestedException.class));
org.hamcrest.CoreMatchers.isA。不在Matchers 类中。
您可以将测试代码包装在 try/catch 块中，捕获抛出的异常，检查内部原因，记录/断言/任何内容，然后重新抛出异常（如果需要）。
【讨论】：
如果您使用的是最新版本的 JUnit，您可以扩展默认测试运行程序来为您处理此问题（无需将每个方法包装在 try/catch 块中）
ExtendedTestRunner.java - 新的测试运行器：
public class ExtendedTestRunner extends BlockJUnit4ClassRunner
{
public ExtendedTestRunner( Class<?> clazz )
throws InitializationError
{
super( clazz );
}
@Override
protected Statement possiblyExpectingExceptions( FrameworkMethod method,
Object test,
Statement next )
{
ExtendedTest annotation = method.getAnnotation( ExtendedTest.class );
return expectsCauseException( annotation ) ?
new ExpectCauseException( next, getExpectedCauseException( annotation ) ) :
super.possiblyExpectingExceptions( method, test, next );
}
@Override
protected List<FrameworkMethod> computeTestMethods()
{
Set<FrameworkMethod> testMethods = new HashSet<FrameworkMethod>( super.computeTestMethods() );
testMethods.addAll( getTestClass().getAnnotatedMethods( ExtendedTest.class ) );
return testMethods;
}
@Override
protected void validateTestMethods( List<Throwable> errors )
{
super.validateTestMethods( errors );
validatePublicVoidNoArgMethods( ExtendedTest.class, false, errors );
}
private Class<? extends Throwable> getExpectedCauseException( ExtendedTest annotation )
{
if (annotation == null || annotation.expectedCause() == ExtendedTest.None.class)
return null;
else
return annotation.expectedCause();
}
private boolean expectsCauseException( ExtendedTest annotation) {
return getExpectedCauseException(annotation) != null;
}
}
ExtendedTest.java - 用于标记测试方法的注释：
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface ExtendedTest
{
/**
* Default empty exception
*/
static class None extends Throwable {
private static final long serialVersionUID= 1L;
private None() {
}
}
Class<? extends Throwable> expectedCause() default None.class;
}
ExpectCauseException.java - 新的 JUnit 语句：
public class ExpectCauseException extends Statement
{
private Statement fNext;
private final Class<? extends Throwable> fExpected;
public ExpectCauseException( Statement next, Class<? extends Throwable> expected )
{
fNext= next;
fExpected= expected;
}
@Override
public void evaluate() throws Exception
{
boolean complete = false;
try {
fNext.evaluate();
complete = true;
} catch (Throwable e) {
if ( e.getCause() == null || !fExpected.isAssignableFrom( e.getCause().getClass() ) )
{
String message = "Unexpected exception cause, expected<"
+ fExpected.getName() + "> but was<"
+ ( e.getCause() == null ? "none" : e.getCause().getClass().getName() ) + ">";
throw new Exception(message, e);
}
}
if (complete)
throw new AssertionError( "Expected exception cause: "
+ fExpected.getName());
}
}
用法：
@RunWith( ExtendedTestRunner.class )
public class MyTests
{
@ExtendedTest( expectedCause = MyException.class )
public void someMethod()
{
throw new RuntimeException( new MyException() );
}
}
【讨论】：
您总是可以手动完成：
@Test
public void someMethod() {
try{
... all your code
} catch (Exception e){
// check your nested clauses
if(e.getCause() instanceof FooException){
// pass
} else {
Assert.fail("unexpected exception");
}
}
【讨论】：
您可以为异常创建一个Matcher。即使您使用像 Arquillian 的 @RunWith(Arquillian.class) 这样的另一个测试运行程序，这也有效，因此您不能使用上面建议的 @RunWith(ExtendedTestRunner.class) 方法。
这是一个简单的例子：
public class ExceptionMatcher extends BaseMatcher<Object> {
private Class<? extends Throwable>[] classes;
// @SafeVarargs // <-- Suppress warning in Java 7. This usage is safe.
public ExceptionMatcher(Class<? extends Throwable>... classes) {
this.classes = classes;
}
@Override
public boolean matches(Object item) {
for (Class<? extends Throwable> klass : classes) {
if (! klass.isInstance(item)) {
return false;
}
item = ((Throwable) item).getCause();
}
return true;
}
@Override
public void describeTo(Description descr) {
descr.appendText("unexpected exception");
}
}
然后将它与@Rule 和ExpectedException 一起使用，如下所示：
@Rule
public ExpectedException thrown = ExpectedException.none();
@Test
public void testSomething() {
thrown.expect(new ExceptionMatcher(IllegalArgumentException.class, IllegalStateException.class));
throw new IllegalArgumentException("foo", new IllegalStateException("bar"));
}
由 Craig Ringer 于 2012 年编辑添加：增强且更可靠的版本：
boolean rethrow 来抛出不匹配的异常。这样可以保留嵌套异常的堆栈跟踪，以便于调试。@SaveVarargs。完整代码：
import org.apache.commons.lang3.exception.ExceptionUtils;
import org.hamcrest.BaseMatcher;
import org.hamcrest.Description;
public class ExceptionMatcher extends BaseMatcher<Object> {
private Class<? extends Throwable>[] acceptedClasses;
private Throwable[] nestedExceptions;
private final boolean rethrow;
@SafeVarargs
public ExceptionMatcher(Class<? extends Throwable>... classes) {
this(false, classes);
}
@SafeVarargs
public ExceptionMatcher(boolean rethrow, Class<? extends Throwable>... classes) {
this.rethrow = rethrow;
this.acceptedClasses = classes;
}
@Override
public boolean matches(Object item) {
nestedExceptions = ExceptionUtils.getThrowables((Throwable)item);
for (Class<? extends Throwable> acceptedClass : acceptedClasses) {
for (Throwable nestedException : nestedExceptions) {
if (acceptedClass.isInstance(nestedException)) {
return true;
}
}
}
if (rethrow) {
throw new AssertionError(buildDescription(), (Throwable)item);
}
return false;
}
private String buildDescription() {
StringBuilder sb = new StringBuilder();
sb.append("Unexpected exception. Acceptable (possibly nested) exceptions are:");
for (Class<? extends Throwable> klass : acceptedClasses) {
sb.append("\n ");
sb.append(klass.toString());
}
if (nestedExceptions != null) {
sb.append("\nNested exceptions found were:");
for (Throwable nestedException : nestedExceptions) {
sb.append("\n ");
sb.append(nestedException.getClass().toString());
}
}
return sb.toString();
}
@Override
public void describeTo(Description description) {
description.appendText(buildDescription());
}
}
典型输出：
java.lang.AssertionError: Expected: Unexpected exception. Acceptable (possibly nested) exceptions are:
class some.application.Exception
Nested exceptions found were:
class javax.ejb.EJBTransactionRolledbackException
class javax.persistence.NoResultException
got: <javax.ejb.EJBTransactionRolledbackException: getSingleResult() did not retrieve any entities.>
【讨论】：
我为此编写了一个小的 JUnit 扩展。静态辅助函数接受一个函数体和一个预期异常数组：
import static org.junit.Assert.assertTrue;
import static org.junit.Assert.fail;
import java.util.Arrays;
public class AssertExt {
public static interface Runnable {
void run() throws Exception;
}
public static void assertExpectedExceptionCause( Runnable runnable, @SuppressWarnings("unchecked") Class[] expectedExceptions ) {
boolean thrown = false;
try {
runnable.run();
} catch( Throwable throwable ) {
final Throwable cause = throwable.getCause();
if( null != cause ) {
assertTrue( Arrays.asList( expectedExceptions ).contains( cause.getClass() ) );
thrown = true;
}
}
if( !thrown ) {
fail( "Expected exception not thrown or thrown exception had no cause!" );
}
}
}
您现在可以像这样检查预期的嵌套异常：
import static AssertExt.assertExpectedExceptionCause;
import org.junit.Test;
public class TestExample {
@Test
public void testExpectedExceptionCauses() {
assertExpectedExceptionCause( new AssertExt.Runnable(){
public void run() throws Exception {
throw new Exception( new NullPointerException() );
}
}, new Class[]{ NullPointerException.class } );
}
}
这样可以避免您一次又一次地编写相同的样板代码。
【讨论】：
最简洁的语法由catch-exception提供：
import static com.googlecode.catchexception.CatchException.*;
catchException(myObj).doSomethingNasty();
assertTrue(caughtException().getCause() instanceof MyException);
【讨论】：
在 JUnit5 中，您可以使用 assertThrows 方法，除了断言抛出的异常之外，它还会返回它，以便您可以对其执行额外的断言。
@Test
void test() {
// Assert that parent exception is thrown and retrieve it
ParentException parentException = assertThrows(ParentException.class, () -> methodThatThrowsException());
// Perform assertions on the cause
Throwable cause = parentException.getCause();
assertThat(cause, ...);
}
void methodThatThrowsException() {
throw new ParentException("foo", new SomeNestedException("bar"));
}
【讨论】：