JUnit：可以“预期” 一个包装的异常？

Question

我知道可以在 JUnit 中定义一个 '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，但具有不同的“嵌套”怎么办？ 原因。

有什么建议么？

Answer 1

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"));
}

Answer 2

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）。

Answer 3

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 - 新测试运行程序：

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() );
    }
}

Answer 4

您始终可以手动执行此操作：

@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");
        }
    }

Answer 5

您可以为异常创建 Matcher 。 即使您使用另一个测试运行器（例如 Arquillian 的 @RunWith(Arquillian.class) 因此您不能使用上面建议的 @RunWith(ExtendedTestRunner.class) 方法。

这是一个简单的示例：

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");
    }
}

然后将其与 @Rule 一起使用和 ExpectedException 像这样：

@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"));
}

添加由 Craig Ringer 在 2012 年编辑：增强且更可靠的版本：

• 基本用法与上面相同
• 可以传递可选的第一个参数布尔重新抛出来抛出不匹配的异常。 这会保留嵌套异常的堆栈跟踪，以便于调试。
• 使用 Apache Commons Lang ExceptionUtils 来处理原因循环并处理某些常见异常使用的非标准异常嵌套类。
• 自描述包括接受的异常
• 失败时的自描述包括遇到的异常的原因堆栈
• 处理 Java 7 警告。 删除旧版本上的@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.>

Answer 6

为此，我编写了一个 JUnit 扩展。 静态辅助函数采用函数体和预期异常数组：

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 } );
    }
}

这可以节省您一次又一次编写相同的样板代码。

Answer 7

在 JUnit5 中，您可以使用assertThrows 方法，该方法除了断言抛出的异常之外，还返回该异常，以便您可以对其执行其他断言。

@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"));
}

Answer 8

catch-exception 提供了最简洁的语法：

import static com.googlecode.catchexception.CatchException.*;

catchException(myObj).doSomethingNasty();
assertTrue(caughtException().getCause() instanceof MyException);

Answer 9

对于所有这些类型的断言，我们在assertj 中有asserThatTownBy。

assertThatThrownBy(() -> blah())
.isInstanceOf(BlahException.class)
.hasCauseExactlyInstanceOf(BlahNestedException.class)
.hasRootCauseMessage("一些消息");