When editing a file using vi, temporary file such as .test.swp file is
created.
As far as I know, it should be deleted automatically after save and
quit editing the file. But it is not.

For example,
1. edit a file name "test"
2. save and exit vi editor with ":wq!"
3. there still remains .test.swp

The .swp file is deleted after pc reboot.

Any clue?