{empty-pair (from-pairs [[]])
 extra (from-pairs [] [])
 later-invalid-pair (from-pairs [[a 1] [b]])
 list-key (from-pairs [[[a] 1]])
 long-pair (from-pairs [[a 1 2]])
 map (from-pairs {a 1})
 map-pair (from-pairs [{a 1}])
 missing (from-pairs)
 non-pair (from-pairs [1])
 null-key (from-pairs [[null a]])
 null-pair (from-pairs [null])
 number-key (from-pairs [[1 a]])
 short-pair (from-pairs [[a]])
 string (from-pairs abc)
 string-pair (from-pairs [ab])}