How to change root logging level programmatically for logback

Try this:

import org.slf4j.LoggerFactory;
import ch.qos.logback.classic.Level;
import ch.qos.logback.classic.Logger;

Logger root = (Logger)LoggerFactory.getLogger(org.slf4j.Logger.ROOT_LOGGER_NAME);
root.setLevel(Level.INFO);

Note that you can also tell logback to periodically scan your config file like this:

<configuration scan="true" scanPeriod="30 seconds" > 
  ...
</configuration> 

I assume you are using logback (from the configuration file).

From logback manual, I see

Logger rootLogger = LoggerFactory.getLogger(org.slf4j.Logger.ROOT_LOGGER_NAME);

Perhaps this can help you change the value?

using logback 1.1.3 I had to do the following (Scala code):

import ch.qos.logback.classic.Logger
import org.slf4j.LoggerFactory    
...
val root: Logger = LoggerFactory.getLogger(org.slf4j.Logger.ROOT_LOGGER_NAME).asInstanceOf[Logger]

As pointed out by others, you simply create mockAppender and then create a LoggingEvent instance which essentially listens to the logging event registered/happens inside mockAppender.

Here is how it looks like in test:

import org.slf4j.LoggerFactory;
import ch.qos.logback.classic.Level;
import ch.qos.logback.classic.Logger;
import ch.qos.logback.classic.spi.ILoggingEvent;
import ch.qos.logback.classic.spi.LoggingEvent;
import ch.qos.logback.core.Appender;

@RunWith(MockitoJUnitRunner.class)
public class TestLogEvent {

// your Logger
private Logger log = (Logger) LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME);

// here we mock the appender
@Mock
private Appender<ILoggingEvent> mockAppender;

// Captor is generic-ised with ch.qos.logback.classic.spi.LoggingEvent
@Captor
private ArgumentCaptor<LoggingEvent> captorLoggingEvent;

/**
 * set up the test, runs before each test
 */
@Before
public void setUp() {
    log.addAppender(mockAppender);
}

/**
 * Always have this teardown otherwise we can stuff up our expectations. 
 * Besides, it's good coding practise
 */
@After
public void teardown() {
    log.detachAppender(mockAppender);
}


// Assuming this is your method
public void yourMethod() {
    log.info("hello world");
}

@Test
public void testYourLoggingEvent() {

    //invoke your method
    yourMethod();

    // now verify our logging interaction
    // essentially appending the event to mockAppender
    verify(mockAppender, times(1)).doAppend(captorLoggingEvent.capture());

    // Having a generic captor means we don't need to cast
    final LoggingEvent loggingEvent = captorLoggingEvent.getValue();

    // verify that info log level is called
    assertThat(loggingEvent.getLevel(), is(Level.INFO));

    // Check the message being logged is correct
    assertThat(loggingEvent.getFormattedMessage(), containsString("hello world"));
}
}