[ticket/11665] Can't change file names already sent to set_filenames

PHPBB3-11665
[ticket/11665] Fix test class name

PHPBB3-11665
Merge remote-tracking branch 'EXreaction/ticket/11665' into develop

* EXreaction/ticket/11665:
  [ticket/11665] Fix test class name
  [ticket/11665] Can't change file names already sent to set_filenames