Logging spy for testin log4j backed logging

gistfile1.java

package au.com.coles.boston.app.service.impl;

import com.google.common.collect.Lists;
import org.apache.log4j.Appender;
import org.apache.log4j.Level;
import org.apache.log4j.Logger;
import org.apache.log4j.spi.LoggingEvent;
import org.mockito.ArgumentCaptor;

import java.util.List;

import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;

public class LoggingSpy {

    private Appender appenderMock = mock(Appender.class);

    private Level originalLevel;

    private Logger logger;

    public LoggingSpy(Class loggedClass, Level logLevelToObserve) {
        logger = Logger.getLogger(loggedClass);
        originalLevel = logger.getLevel();
        logger.addAppender(appenderMock);
        logger.setLevel(logLevelToObserve);
    }

    public String observedMessage() {
        ArgumentCaptor<LoggingEvent> loggingEventCaptor = ArgumentCaptor.forClass(LoggingEvent.class);
        verify(appenderMock).doAppend(loggingEventCaptor.capture());
        return loggingEventCaptor.getValue().getMessage().toString();
    }

    public List<String> observedMessages(int numExpectedMessages) {
        ArgumentCaptor<LoggingEvent> loggingEventCaptor = ArgumentCaptor.forClass(LoggingEvent.class);
        verify(appenderMock, times(numExpectedMessages)).doAppend(loggingEventCaptor.capture());

        List<String> messages = Lists.newArrayList();
        for (LoggingEvent loggingEvent : loggingEventCaptor.getAllValues()) {
            messages.add(loggingEvent.getMessage().toString());
        }
        return messages;
    }

    public Throwable observedThrowable() {
        ArgumentCaptor<LoggingEvent> loggingEventCaptor = ArgumentCaptor.forClass(LoggingEvent.class);
        verify(appenderMock).doAppend(loggingEventCaptor.capture());
        return loggingEventCaptor.getValue().getThrowableInformation().getThrowable();
    }

    public void restoreLogLevel() {
        logger.setLevel(originalLevel);
    }
}