How to intercept SLF4J (with logback) logging via a JUnit test?

Question

Is it possible to somehow intercept the logging (SLF4J + logback) and get an InputStream (or something else that is readable) via a JUnit test case...?

Answer 1

You can use slf4j-test from http://projects.lidalia.org.uk/slf4j-test/. It replaces the entire logback slf4j implementation by it's own slf4j api implementation for tests and provides an api to assert against logging events.

example:

  
    
      maven-surefire-plugin
      
        
          ch.qos.logback:logback-classic
        
      
    
  


public class Slf4jUser {

    private static final Logger logger = LoggerFactory.getLogger(Slf4jUser.class);

    public void aMethodThatLogs() {
        logger.info("Hello World!");
    }
}

public class Slf4jUserTest {

    Slf4jUser slf4jUser = new Slf4jUser();
    TestLogger logger = TestLoggerFactory.getTestLogger(Slf4jUser.class);

    @Test
    public void aMethodThatLogsLogsAsExpected() {
        slf4jUser.aMethodThatLogs();

        assertThat(logger.getLoggingEvents(), is(asList(info("Hello World!"))));
    }

    @After
    public void clearLoggers() {
        TestLoggerFactory.clear();
    }
}