Use ERROR instead of an ECASE form with no clauses.
SBCL outputs compilation warnings for ECASE forms missing clauses and that
causes Quicklisp test failures.
    
        | author | Robert Brown <robert.brown@gmail.com> | 
    
        | date | Sat, 04 Nov 2023 10:42:34 -0400 | 
    
    
        | parents | e5e1471cb234 | 
    
        | children | (none) | 
    
        | branches/tags | default tip | 
    
        | files | test/tests.lisp | 
Changes
    
--- a/test/tests.lisp	Wed Jun 21 15:21:05 2023 -0400
+++ b/test/tests.lisp	Sat Nov 04 10:42:34 2023 -0400
@@ -338,9 +338,11 @@
                 (b . c) (b . d)
                 (e . f))
               (edges g))))
-  (let ((g (build-from-roots '() (lambda (v) (ecase v)))))
+  (let ((g (build-from-roots '() (lambda (v)
+                                   (error "predecessor called on ~S" v)))))
     (is (same '() (vertices g)))
     (is (same '() (edges g))))
-  (let ((g (build-from-leafs '() (lambda (v) (ecase v)))))
+  (let ((g (build-from-leafs '() (lambda (v)
+                                   (error "predecessor called on ~S" v)))))
     (is (same '() (vertices g)))
     (is (same '() (edges g)))))