Mockito Unit test lombok.extern.slf4j @Slf4j annotation log?

Question

I have a method that calls a method called "burn" inside that throws a data exception, and if so, then it is caught in a try/catch block and logs to a logger. The class is using the annotation @Slf4j however, and lombok.extern.slf4j:

@Slf4j
public class MyClass {

 private void myMethod(Type parameter) throws Exception {
     try {
        dataGateway.burn(id);
         }
     catch {
        log.error("Failed to burn({})",id);
        }
  }

I have already mocked the datagateway and have it throwing an exception when burn is called, I know the exception is caught but how do I use verify to assert the logger was called with .error?? DateGateway dBMock = mock(DateGateway.class);

when(dBMock.burn(anyString())).thenReturn(new DataException("exception"));

score 5 · Answer 1 · answered Oct 19 '20 at 13:09

5

I found a nice solution to this problem here: https://www.jvt.me/posts/2019/09/22/testing-slf4j-logs/

The solution was to add a log appender to the class you want to test and then just read what has been logged from that appender.

Here is a generic method to add and return an appender for a specific class:

private ListAppender<ILoggingEvent> getListAppenderForClass(Class clazz) {
    Logger logger = (Logger) LoggerFactory.getLogger(clazz);
    ListAppender<ILoggingEvent> loggingEventListAppender = new ListAppender<>();
    loggingEventListAppender.start();
    logger.addAppender(loggingEventListAppender);
    return loggingEventListAppender;
}

In your case you could then use this appender like this in your test to verify that your specific log row was invoked:

final ListAppender<ILoggingEvent> listAppenderForClass = getListAppenderForClass(CardApi.class);
org.assertj.core.api.Assertions.assertThat(listAppenderForClass.list)
                .extracting(ILoggingEvent::getFormattedMessage)
                .anyMatch((Predicate<String>) s -> s.startsWith("Failed to burn"));

answered Oct 19 '20 at 13:09

Fredrik

487
5
12

1

You solution cannot be applied to Lombok @Slf4j, The provided Logger does not provide addAppender method. – spekdrum Dec 10 '20 at 08:03
@spekdrum: That is strange. I am running the exact code above with Slf4j annotation from Lombok 1.18.12. – Fredrik Dec 10 '20 at 13:51
@Fredik I'm using Lombok 1.18.16. LoggerFactory and Logger from Slf4 1.7.30. – spekdrum Dec 14 '20 at 07:30
This approach did work for me using Lombok 1.18.16. – Radioactive Jan 08 '21 at 22:42
1

@spekdrum: You should use Logger class from ch.qos.logback.classic.Logger and not the one from sl4j – korgoth Mar 15 '21 at 10:21
similar approach https://stackoverflow.com/a/69840927/7188713 – Ashish Mishra Sep 28 '22 at 09:25

score 3 · Answer 2 · answered Jul 31 '21 at 07:48

3

You can try library: https://www.simplify4u.org/slf4j-mock/

It is also work with lombok annotation.

With slf4j-mock you don't need special code for preparing logger mock.

answered Jul 31 '21 at 07:48

Slawomir Jaranowski

7,381
3
25
33

Very easy to use, I appreciated the documentation that covered many use cases and got my logs tested in no time. – Cristina_eGold Oct 18 '21 at 02:35

Mockito Unit test lombok.extern.slf4j @Slf4j annotation log?

2 Answers2