Test ab-err-xs0006-003

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" version="3.0">
   <p:output port="result">
      <result/>
   </p:output>
   <p:identity>
      <p:with-input>
         <source/>
      </p:with-input>
   </p:identity>
   <p:choose>
      <p:when test="true()">
         <p:output port="result"/>
         <p:sink/>
      </p:when>
      <p:otherwise>
         <p:output port="result"/>
         <p:identity>
            <p:with-input>
               <otherwise/>
            </p:with-input>
         </p:identity>
      </p:otherwise>
   </p:choose>
</p:declare-step>