我可以在一种测试方法中测试多个抛出的异常吗？

Question

我有一个明确指定的接口，我为此编写了我的 JUnit 测试：

public interface ShortMessageService {

     /**
     * Creates a message. A message is related to a topic
     * Creates a date for the message
     * @throws IllegalArgumentException, if the message is longer then 255 characters.
     * @throws IllegalArgumentException, if the message ist shorter then 10 characters.
     * @throws IllegalArgumentException, if the user doesn't exist
     * @throws IllegalArgumentException, if the topic doesn't exist
     * @throws NullPointerException, if one argument is null.
     * @param userName
     * @param message
     * @return ID of the new created message
     */
     Long createMessage(String userName, String message, String topic);

[...]

}

如您所见，实现可能会引发各种异常，我必须为此编写测试。我目前的方法是为接口中指定的一种可能的异常编写一种测试方法，如下所示：

public abstract class AbstractShortMessageServiceTest
{

    String message;
    String username;
    String topic;

    /**
     * @return A new empty instance of an implementation of ShortMessageService.
     */
    protected abstract ShortMessageService getNewShortMessageService();

    private ShortMessageService messageService;

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

    @Before
    public void setUp() throws Exception
    {
        messageService = getNewShortMessageService();
        message = "Test Message";
        username = "TestUser";
        topic = "TestTopic";
    }

    @Test
    public void testCreateMessage()
    {
        assertEquals(new Long(1L), messageService.createMessage(username, message, topic));
    }

    @Test (expected = IllegalArgumentException.class)
    public void testCreateMessageUserMissing() throws Exception
    {
        messageService.createMessage("", message, topic);
    }

    @Test (expected = IllegalArgumentException.class)
    public void testCreateMessageTopicMissing() throws Exception
    {
        messageService.createMessage(username, message, "");
    }

    @Test (expected = IllegalArgumentException.class)
    public void testCreateMessageTooLong() throws Exception
    {
        String message = "";
        for (int i=0; i<255; i++) {
            message += "a";
        }
        messageService.createMessage(username, message, topic);
    }


    @Test (expected = IllegalArgumentException.class)
    public void testCreateMessageTooShort() throws Exception
    {
        messageService.createMessage(username, "", topic);
    }

    @Test (expected = NullPointerException.class)
    public void testCreateMessageNull() throws Exception
    {
        messageService.createMessage(username, null, topic);
    }

[...]

}

所以现在我必须为接口中定义的那个方法定义很多测试方法，这感觉很尴尬。我可以将所有这些异常测试组合到一种测试方法中吗？或者最佳做法是什么？

Answer 1

将它们全部组合在一个方法中可能不是最好的主意，因为您不会真正知道哪个测试用例引发了哪个异常。

例如，如果你有这条线

messageService.createMessage(username, null, topic);

应该抛出一个NullPointerException，但它却抛出了一个IllegalArgumentException，你不希望这算作成功。

如果您想在一个测试用例中测试该方法的所有异常，那么一个不错的选择是将每个异常测试包装在 try..catch 块中。

例如，你可以有

@Test
public void testCreateMessageExceptions() {
    // test #1: a null message
    try {
        messageService.createMessage(username, null, topic);
        // if it got this far, that's a problem!
        fail();
    } catch(NullPointerException e) {
        // great, that's what it's meant to do! continue testing
    } catch(Exception e) {
        // if it threw the wrong type of exception, that's a problem!
        fail();
    }

    // test #2: an empty user
    try {
        messageService.createMessage("", message, topic);
        fail();
    } catch(IllegalArgumentException e) {

    } catch(Exception e) {
        fail();
    }

    // ...
}

Answer 2

很遗憾，@Test 注解不允许捕获多种异常类型（api 参考 http://junit.sourceforge.net/javadoc/org/junit/Test.html）。

作为第一个选项，我会提倡迁移到 TestNG。如果您的团队不允许这样做，您可以在 JUnit 中做一些事情。

一定要使用参数化测试用例，这样您就不必为每个测试用例编写一个测试函数 (http://junit.sourceforge.net/javadoc/org/junit/runners/Parameterized.html)。从这里开始，有几个选项。

1. 按异常类型对测试数据进行分组。

   @Test (expected = IllegalArgumentException.class)
   public void testIllegalArgumentException(String username, String message, String topic) {}
   
   @Test (expected = NullPointerException.class)
   public void testNullPointerException(String username, String message, String topic) {}
   

2. 在您的方法签名中组合异常类型。 （这是我推荐的）下面的粗略轮廓......

   public void testException(String username, String message, String topic, Class<? extends Exception>[] expectedExceptionClasses) {
       try {
           // exception throwing code
       } catch (Exception e) {
           boolean found = false;
           for (Class<?> expectedException : expectedExceptions) {
               if (e instanceof expectedException) {
                   found = true;
               }
           }
           if (found) {
               return;
           }
       }
       Assert.fail();
   }
   

3. 将所有测试放在 Exception 类下（我感觉你不想这样做。）。

   @Test (expected = Exception.class)
   public void testException(String username, String message, String topic) {}