Problem:    NOCOMPOUNDSUGS entry in spell file not tested.
Solution:   Add a test. (Dominique Pellé, closes vim/vim#8624)
https://github.com/vim/vim/commit/9c9472ff49b09c3d8f747b330eeb1cdb92bab449

Problem:    Spellfile functionality not fully tested.
Solution:   Add tests for CHECKCOMPOUNDPATTERN and COMMON. (Dominique Pellé,
            closes vim/vim#8270)
https://github.com/vim/vim/commit/dc3275a1ac73b6c4d0c9d2e238ea80b477705b6f

Problem:    There is :spellwrong and :spellgood but not :spellrare.
Solution:   Add :spellrare. (Martin Tournoij, closes vim/vim#4291)
https://github.com/vim/vim/commit/08cc374dabd2a02785129fa1c0100f7745c244ad