src/it/test6/build.xml

<?xml version="1.0"?>
<project name="test6">

    <target name="test">

        <!-- <taskdef name="antlr" classname="org.apache.tools.ant.taskdefs.optional.ANTLR"/> -->

        <mkdir dir="target" />
        <antlr target="calc.g" outputdirectory="target">
            <classpath refid="maven.plugin.classpath"/>
        </antlr>

    </target>

</project>