ktlint-test/src/main/resources/logback-test.xml

<configuration>
    <if condition='property("KTLINT_UNIT_TEST_TRACE").equalsIgnoreCase("on")'>
        <then>
            <property name="level" value="trace" />
        </then>
        <else>
            <property name="level" value="debug" />
        </else>
    </if>
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <!-- encoders are assigned the type
             ch.qos.logback.classic.encoder.PatternLayoutEncoder by default -->
        <encoder>
            <!-- Keep logging output of unit test as minimal as possible-->
            <pattern>[%level] %logger{36} - %msg%n</pattern>
        </encoder>
    </appender>

    <root level="${level}">
        <appender-ref ref="STDOUT" />
    </root>
</configuration>