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| 1 | +## JUnit如何断言一个确定的异常抛出 |
| 2 | + |
| 3 | +#### 问题 |
| 4 | + |
| 5 | +在JUnit4单元测试中,我要怎样做才能测试出有特定的异常抛出?我能想到的就只有下面的方法: |
| 6 | + |
| 7 | +```java |
| 8 | +@Test |
| 9 | +public void testFooThrowsIndexOutOfBoundsException() { |
| 10 | + boolean thrown = false; |
| 11 | + |
| 12 | + try { |
| 13 | + foo.doStuff(); |
| 14 | + } catch (IndexOutOfBoundsException e) { |
| 15 | + thrown = true; |
| 16 | + } |
| 17 | + |
| 18 | + assertTrue(thrown); |
| 19 | +} |
| 20 | +``` |
| 21 | + |
| 22 | +#### 回答1 |
| 23 | + |
| 24 | +在JUnit4后支持下面的写法: |
| 25 | +```java |
| 26 | +@Test(expected=IndexOutOfBoundsException.class) |
| 27 | +public void testIndexOutOfBoundsException() { |
| 28 | + ArrayList emptyList = new ArrayList(); |
| 29 | + Object o = emptyList.get(0); |
| 30 | +} |
| 31 | +``` |
| 32 | +(译者:在`@Test`注解内提供了`expected`属性,你可以用它来指定一个`Throwble`类型,如果方法调用中抛出了这个异常,那么这条测试用例就相当于通过了) |
| 33 | + |
| 34 | +#### 回答2 |
| 35 | + |
| 36 | +如果你使用的是JUnit4.7,你可以使用如下的期望异常规则来验证异常信息: |
| 37 | + |
| 38 | +```java |
| 39 | +public class FooTest { |
| 40 | + @Rule |
| 41 | + public final ExpectedException exception = ExpectedException.none(); |
| 42 | + |
| 43 | + @Test |
| 44 | + public void doStuffThrowsIndexOutOfBoundsException() { |
| 45 | + Foo foo = new Foo(); |
| 46 | + |
| 47 | + exception.expect(IndexOutOfBoundsException.class); |
| 48 | + foo.doStuff(); |
| 49 | + } |
| 50 | +} |
| 51 | +``` |
| 52 | + |
| 53 | +这种方式比`@Test(expected=IndexOutOfBoundsException.class)`要更好,如果是在调用`foo.doStuff()`方法之前就已经抛出异常的话,测试结果就不是我们想要的了。 |
| 54 | +(译者:同时,`ExpectedException`还能够验证异常信息,如`exception.expectMessage("there is an exception!");` |
| 55 | + |
| 56 | +#### 拓展阅读 |
| 57 | + |
| 58 | +1. [JUnit:使用ExpectedException进行异常测试](http://www.tuicool.com/articles/ANviIz) |
| 59 | +2. [JUnit4 用法详解](http://www.blogjava.net/jnbzwm/archive/2010/12/15/340801.html) |
| 60 | + |
| 61 | +#### StackOverflow地址: |
| 62 | + |
| 63 | +[http://stackoverflow.com/questions/156503/how-do-you-assert-that-a-certain-exception-is-thrown-in-junit-4-tests](http://stackoverflow.com/questions/156503/how-do-you-assert-that-a-certain-exception-is-thrown-in-junit-4-tests) |
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