Merge pull request #5027 from tony612/add-files-completion-to-mix-test

add files completion to mix test

plugins/mix/_mix

@@ -73,6 +73,10 @@ case $state in
     case $line[1] in
       (help)
          _arguments ':feature:__task_list'
+         ;;
+      (test)
+         _files
+         ;;
     esac
   ;;
 esac