; Improve and add tests for Completion Preview mode

; Improve and add tests for Completion Preview mode

Fix handling of capfs that return a function or signal an error,
respect the ':exclusive' completion property, fix lingering "exact"
face after deletion that makes the matches non-exact, and add tests.

* lisp/completion-preview.el (completion-preview--make-overlay): Only
reuse the previous 'after-string' if it has the right face.
(completion-preview--try-table)
(completion-preview--capf-wrapper): New functions.
(completion-preview--update): Use them.
* test/lisp/completion-preview-tests.el: New file.  (Bug#67275)