如何使用 junit 测试 log4j 是否记录了警告? [英] How can I test with junit that a warning was logged with log4j?

问题描述

我正在测试一种方法，该方法在出现问题时记录警告并返回 null.
类似的东西:

I'm testing a method that logs warnings when something went wrong and returns null.
something like:

private static final Logger log = Logger.getLogger(Clazz.class.getName());
....
if (file == null || !file.exists()) {
  // if File not found
  log.warn("File not found: "+file.toString());
} else if (!file.canWrite()) {
  // if file is read only
  log.warn("File is read-only: "+file.toString());
} else {
  // all checks passed, can return an working file.
  return file;
}
return null;

我想用 junit 测试是否发出警告，除了返回 null 外，在所有情况下(例如，找不到文件，文件是只读的).
有什么想法吗?
谢谢，阿萨夫:-)

i'd like to test with junit that a warning was issued, in addition to returning null, in all cases (e.g. file not found, file is read-only).
any ideas?
thanks, asaf :-)

我对 Aaron 的回答的实现(加上 peter 的评论):

My implementation of Aaron's answer (plus peter's remark):

public class UnitTest {
...

@BeforeClass
public static void setUpOnce() {
  appenders = new Vector<Appender>(2);
  // 1. just a printout appender:
  appenders.add(new ConsoleAppender(new PatternLayout("%d [%t] %-5p %c - %m%n")));
  // 2. the appender to test against:
  writer = new StringWriter();
  appenders.add(new WriterAppender(new PatternLayout("%p, %m%n"),writer));
}

@Before
public void setUp() {
  // Unit Under Test:
  unit = new TestUnit();
  // setting test appenders:
  for (Appender appender : appenders) {
    TestUnit.log.addAppender(appender);
  }
  // saving additivity and turning it off:
  additivity = TestUnit.log.getAdditivity();
  TestUnit.log.setAdditivity(false);
}

@After
public void tearDown() {
  unit = null;
  for (Appender appender : appenders) {
    TestUnit.log.removeAppender(appender);
  }
  TestUnit.log.setAdditivity(additivity);
}

@Test
public void testGetFile() {
  // start fresh:
  File file;
  writer.getBuffer().setLength(0);

  // 1. test null file:
  System.out.println(" 1. test null file.");
  file = unit.getFile(null);
  assertNull(file);
  assertTrue(writer.toString(), writer.toString().startsWith("WARN, File not found"));
  writer.getBuffer().setLength(0);

  // 2. test empty file:
  System.out.println(" 2. test empty file.");
  file = unit.getFile("");
  assertNull(file);
  assertTrue(writer.toString(), writer.toString().startsWith("WARN, File not found"));
  writer.getBuffer().setLength(0);
}

谢谢各位，

推荐答案

在单元测试的设置中:

1. 获取相同的记录器
2. 使其无添加

3. 添加一个能够记住列表中消息的 appender:

1. Get the same logger
2. Make it non-additive

3. Add an appender which remembers the messages in a list:

public class TestAppender extends AppenderSkeleton {
    public List<String> messages = new ArrayList<String>();

    public void doAppend(LoggingEvent event) {
        messages.add( event.getMessage().toString() );
    }
}

将 appender 添加到记录器

Add the appender to the logger

现在您可以调用您的代码了.测试后，您将在列表中找到所有日志消息.如果需要，请添加日志级别 (messages.add( event.getLevel() + " " + event.getMessage() );).

Now you can call your code. After the test, you will find all log messages in the list. Add the log level if you want (messages.add( event.getLevel() + " " + event.getMessage() );).

在tearDown()中，再次移除appender并启用可加性.

In tearDown(), remove the appender again and enable additivity.

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