ant/src/etc/testcases/core/unknownelement.xml

<project>
  <target name="testMaybeConfigure">
    <taskdef name="parent" 
             classname="org.apache.tools.ant.UnknownElementTest$Parent"
             loaderref="unknown.id">
      <classpath>
        <pathelement location="../../../../build/testcases"/>
        <pathelement path="${java.class.path}"/>
      </classpath>
    </taskdef>
    <taskdef name="child"
             classname="org.apache.tools.ant.UnknownElementTest$Child"
             loaderref="unknown.id"/>
    <parent>
      <child/>
      <child/>
    </parent>
  </target>
</project>