anchor.diff:                                   (htree:value entry)
                                    (length nodes))))
   
  -             (htree:entries tree))))
  +             (htree:entries history))))
   
   (prove:subtest "Visit all nodes until distant node"
  -  (let* ((history (make-tree1))
  +  (let* ((history (make-history1))
            (creator (htree:current-owner-identifier history))
            (distant-node-value "http://example.root/A1")
            (distant-node (first (htree:find-nodes history distant-node-value))))
  
positive.code:                              '("http://child/A3a" nil)
                               '("http://child/A3b" nil)))
        (prove:is (alexandria:hash-table-keys
                   (htree:bindings (first (htree:find-nodes tree (first url-owner)))))
                  (if (second url-owner)
                      (list (htree:owner tree (second url-owner)))
                      nil)))
  
      (htree:delete-owner tree "parent-owner")
      (prove:is (htree:current-owner-identifier tree)
                htree:+default-owner+)
      (prove:is (htree:owner tree "parent-owner")
                nil)
      (prove:is (hash-table-count (htree:entries tree))
                9)
  
      (maphash (lambda (entry nodes)
  
negative.code: 
  (prove:subtest "Traverse parents."
    (prove:is (htree:all-parents-data
               (htree:back (make-history1)))
              '("http://example.root")))
  
  (prove:subtest "Traverse forward children."
    (prove:is (htree:all-forward-children-data
               (htree:back (make-history1)))
              '("http://example.root/B2")))
  
  (prove:subtest "Traverse all children."
    (prove:is (htree:all-children-data
               (htree:back (make-history1)))
              '("http://example.root/B2" "http://example.root/B1")))
  
  (prove:subtest "Move node to forward-child on add."
    (let ((history (make-history2)))
      (prove:is (htree:value (htree:current-owner-node history))
                "http://example.root/B")
      (htree:back history)
      (prove:is (htree:value (htree:current-owner-node history))
                "http://example.root")
      (htree:add-child "http://example.root/A" history)
      (prove:is (htree:value (htree:current-owner-node history))
                "http://example.root/A")))
  
  (define-class web-page ()
  