In KAutoSaveFilePrivate::tempFile() the name of the kautosavefile that's
going to be created is generated using the filename and the absolute path
and some other bits (e.g. a string generated using KRandom). The problem
with that approach is that sometimes really long filenames can get created.
This unit test ensures that the checks in tempFile() work correctly and
generate filenames that don't exceed NAME_MAX (255 bytes/chars for Linux),
otherwise the files can't be opened.
Depends on D24489