Add tests for uniquify-files, fix bug

* lisp/uniquify-files.el (uniq-file--hilit): Remove previously applied
faces.

* test/lisp/progmodes/uniquify-files-resources/: New directory.

* test/lisp/progmodes/uniquify-files-test.el: New file.
2 jobs for scratch/project-uniquify-files in 59 minutes and 27 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #1428
test-all

00:59:27

passed #1429
test-filenotify-gio

00:44:17

 
Name Stage Failure
failed
test-all Test
Makefile:313: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 1
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:288: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:962: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1