anchor.diff:      ;; TODO: Go to other child.
       ))
   
  -(prove:subtest
  -    "Simple branching tree tests."
  +(prove:subtest "Simple branching tree tests."
     (prove:is (htree:value (htree:current-owner-node (make-tree1)))
               "http://example.root/B2"))
   
  -(prove:subtest
  -    "History depth."
  +(prove:subtest "History depth."
     (prove:is (htree:depth (make-tree1))
               2))
   
  -(prove:subtest
  -    "History size."
  +(prove:subtest "History size."
     (prove:is (htree:size (make-tree1))
               7))
   
  -(prove:subtest
  -    "All contiguous history nodes for current owner."
  +(prove:subtest "All contiguous history nodes for current owner."
     (prove:is (htree:all-contiguous-owned-nodes-data (make-tree1))
               '("http://example.root"
                 "http://example.root/B"
  
positive.code:               "http://example.root/A"
                "http://example.root/A2" "http://example.root/A1")))
  
  (prove:subtest
      "Visiting other branches should not reorder the nodes."
    (prove:is (htree:all-contiguous-owned-nodes-data
               (htree:go-to-child
                 "http://example.root/A2"
  
negative.code:               "http://example.root/A"
                "http://example.root/A2" "http://example.root/A1")))
  
  ;; TODO: Irrelevant?
  ;; (prove:subtest
  ;;     "Reorder manually set current node."
  ;;   (prove:is (htree:all-contiguous-owned-nodes-data
  ;;              (let* ((history (make-tree2))
  ;;                     (second-child (second (htree:children
  ;;                                            (htree:current-owner-node (htree:back history))))))
  ;;                (setf (htree:current-owner-node history) second-child)
  ;;                (htree:back history)
  ;;                history))
  ;;             '("http://example.root"
  ;;               "http://example.root/A"
  ;;               "http://example.root/B")))
  
  (prove:subtest "Traverse parents."
    (prove:is (htree:parent-nodes-data
               (htree:back (make-tree1)))
              '("http://example.root")))
  
  (prove:subtest "Traverse forward children."
    (prove:is (htree:forward-children-nodes-data
               (htree:back (make-tree1)))
              '("http://example.root/B2")))
  
  ;; (prove:subtest
  ;;     "Traverse all children."
  