log4j-to-slf4j/src/test/resources/logback-slf4j.xml

<?xml version="1.0" encoding="UTF-8"?>
<configuration>

  <appender name="LIST" class="ch.qos.logback.core.testUtil.StringListAppender">
    <layout class="ch.qos.logback.classic.PatternLayout">
      <Pattern>%X{TestYear}%msg</Pattern>
    </layout>
  </appender>

  <root level="trace">
    <appender-ref ref="LIST" />
  </root>
</configuration>