refactor + some extra tests

engine/core.scm

@@ -363,8 +363,8 @@
   (assert (symbol? queue-name))
   (assert (integer? layer))
   (assert (procedure? thunk))
-  (set! (hash-table-ref render-queues queue-name)
-    (cons (cons layer thunk) (hash-table-ref render-queues queue-name))))
+  (hash-table-set! render-queues queue-name
+		   (cons (cons layer thunk) (hash-table-ref render-queues queue-name))))
 
 ;; Evaluate a single render queue with a specific mode.
 ;; Render objects are sorted by their layer

test/engine.scm

@@ -88,6 +88,11 @@
 ;; Render queue tests
 (check (hash-table-size render-queues) => 3)
 (check (length render-priority) => 3)
+
+(register-render-queue 'screen2 'screen)
+(check (hash-table-size render-queues) => 4)
+(check (length render-priority) => 4)
+
 (check (length (hash-table-ref render-queues 'screen)) => 0)
 
 (push-render-object 'screen 0 (lambda () #t))