Test nw-err-xs0015-005

The pipeline

<p:declare-step xmlns:err="http://www.w3.org/ns/xproc-error"
                xmlns:ex="http://test" xmlns:p="http://www.w3.org/ns/xproc"
                xmlns:t="http://xproc.org/ns/testsuite/3.0" version="3.0">
   <p:output port="result"/>
   <p:choose>
      <p:when test="true()">
         <p:identity>
            <p:with-input>
               <doc/>
            </p:with-input>
         </p:identity>
      </p:when>
      <p:otherwise/>
   </p:choose>
</p:declare-step>