you need to enable the ASMA to populate the filename based on the Praveen's code.
Map the DCTechnical Name to constant - Filename , so your mapping output should be
<DCValue DCNameSpace="http://sap.com/xi/XI/System/File" DCTechnicalName="FileName">test file</DCValue>
Code will take the input parameters DCtechnical and DC namespace from the mapping and set the values accordingly.