如何使用JUnit来测试某些代码是否抛出异常?

我当然可以这样做:

@Test
public void testFooThrowsIndexOutOfBoundsException() {
  boolean thrown = false;

  try {
    foo.doStuff();
  } catch (IndexOutOfBoundsException e) {
    thrown = true;
  }

  assertTrue(thrown);
}

我记得,对于这类情况,有一个注释或Assert.xyz之类的东西远没有JUnit那么笨拙,更符合JUnit的精神。


当前回答

为了解决同样的问题,我设立了一个小项目:http://code.google.com/p/catch-exception/

使用这个小助手,您可以编写

verifyException(foo, IndexOutOfBoundsException.class).doStuff();

这比JUnit 4.7的ExpectedException规则更详细。与skaffman提供的解决方案相比,您可以指定期望在哪行代码中出现异常。我希望这有帮助。

其他回答

Junit4与Java8的解决方案是使用此功能:

public Throwable assertThrows(Class<? extends Throwable> expectedException, java.util.concurrent.Callable<?> funky) {
    try {
        funky.call();
    } catch (Throwable e) {
        if (expectedException.isInstance(e)) {
            return e;
        }
        throw new AssertionError(
                String.format("Expected [%s] to be thrown, but was [%s]", expectedException, e));
    }
    throw new AssertionError(
            String.format("Expected [%s] to be thrown, but nothing was thrown.", expectedException));
}

用法如下:

    assertThrows(ValidationException.class,
            () -> finalObject.checkSomething(null));

注意,唯一的限制是在lambda表达式中使用最终对象引用。此解决方案允许使用@test(expected=IndexOutOfBoundsException.class)解决方案继续测试断言,而不是期望在方法级别可以执行。

BDD风格解决方案:JUnit 4+Catch异常+AssertJ

import static com.googlecode.catchexception.apis.BDDCatchException.*;

@Test
public void testFooThrowsIndexOutOfBoundsException() {

    when(() -> foo.doStuff());

    then(caughtException()).isInstanceOf(IndexOutOfBoundsException.class);

}

依赖关系

eu.codearte.catch-exception:catch-exception:2.0

除了NamShubWriter所说的,还要确保:

ExpectedException实例是公共的(相关问题)ExpectedException未在@Before方法中实例化。这篇文章清楚地解释了JUnit执行顺序的所有复杂性。

不要这样做:

@Rule    
public ExpectedException expectedException;

@Before
public void setup()
{
    expectedException = ExpectedException.none();
}

最后,这篇博客文章清楚地说明了如何断言抛出了某个异常。

我在Mkyong博客中找到了Junit 4最灵活、最优雅的答案。它具有使用@Rule注释的try/catch的灵活性。我喜欢这种方法,因为您可以读取自定义异常的特定属性。

package com.mkyong;

import com.mkyong.examples.CustomerService;
import com.mkyong.examples.exception.NameNotFoundException;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.ExpectedException;

import static org.hamcrest.CoreMatchers.containsString;
import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.Matchers.hasProperty;

public class Exception3Test {

    @Rule
    public ExpectedException thrown = ExpectedException.none();

    @Test
    public void testNameNotFoundException() throws NameNotFoundException {

        //test specific type of exception
        thrown.expect(NameNotFoundException.class);

        //test message
        thrown.expectMessage(is("Name is empty!"));

        //test detail
        thrown.expect(hasProperty("errCode"));  //make sure getters n setters are defined.
        thrown.expect(hasProperty("errCode", is(666)));

        CustomerService cust = new CustomerService();
        cust.findByName("");

    }

}

我在这里尝试了许多方法,但它们要么很复杂,要么不太符合我的要求。事实上,可以非常简单地编写一个助手方法:

public class ExceptionAssertions {
    public static void assertException(BlastContainer blastContainer ) {
        boolean caughtException = false;
        try {
            blastContainer.test();
        } catch( Exception e ) {
            caughtException = true;
        }
        if( !caughtException ) {
            throw new AssertionFailedError("exception expected to be thrown, but was not");
        }
    }
    public static interface BlastContainer {
        public void test() throws Exception;
    }
}

这样使用:

assertException(new BlastContainer() {
    @Override
    public void test() throws Exception {
        doSomethingThatShouldExceptHere();
    }
});

零依赖:无需mockito,无需powermock;在期末考试中表现很好。