Log4j2 InMemoryAppender for tests

InMemoryAppender.java

package log.appender;

import org.apache.logging.log4j.core.Filter;
import org.apache.logging.log4j.core.Layout;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.appender.AbstractAppender;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.config.plugins.PluginAttribute;
import org.apache.logging.log4j.core.config.plugins.PluginElement;
import org.apache.logging.log4j.core.config.plugins.PluginFactory;
import org.apache.logging.log4j.core.layout.PatternLayout;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;


@Plugin(name = "InMemoryAppender", category = "Core", elementType = "appender", printObject = true)
public class InMemoryAppender extends AbstractAppender {

    public static final Map<String, List<LogEvent>> logEvents = new HashMap<>();

    protected InMemoryAppender(String name, Filter filter, Layout<? extends Serializable> layout) {
        this(name, filter, layout, true);
    }

    public InMemoryAppender(String name, Filter filter, Layout<? extends Serializable> layout, boolean ignoreExceptions) {
        super(name, filter, layout, ignoreExceptions);
    }

    @Override
    public void append(LogEvent logEvent) {
        String loggerName = logEvent.getLoggerName();
        if (!logEvents.containsKey(loggerName)) {
            logEvents.put(loggerName, new ArrayList<LogEvent>());
        }
        logEvents.get(loggerName).add(logEvent);
    }

    @PluginFactory
    public static InMemoryAppender createAppender(
            @PluginAttribute("name") String name,
            @PluginElement("Layout") Layout<? extends Serializable> layout,
            @PluginElement("Filter") final Filter filter,
            @PluginAttribute("otherAttribute") String otherAttribute) {
        if (name == null) {
            LOGGER.error("No name provided for MyCustomAppenderImpl");
            return null;
        }
        if (layout == null) {
            layout = PatternLayout.createDefaultLayout();
        }
        return new InMemoryAppender(name, filter, layout, true);
    }

}

log4j2.xml

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
    <Appenders>
        <InMemoryAppender name="testAppender"/>
    </Appenders>
    <Loggers>
        <Logger name="app.logger" level="trace">
            <AppenderRef ref="testAppender"/>
        </Logger>
        <Root level="off"/>
    </Loggers>
</Configuration>