var doc = app.activeDocument;   
if (app.selection.length == 0 || app.selection[0].constructor.name != "TextFrame") exit();   
var textFrame = app.selection[0];   
var assignmentFile = new File("~/Desktop/Test.icma");   
var incopyFile = new File("~/Desktop/Test.icml");   
var assignment = doc.assignments.add(assignmentFile, {name:"Test2"});   
var unassignedContent = doc.assignments[doc.assignments.length-1];   
textFrame.texts[0].exportFile(ExportFormat.INCOPY_MARKUP, incopyFile);   
unassignedContent.assignedStories[0].move(LocationOptions.AT_END, assignment);   
assignment.update();