.

wcfs/internal/xbtree.py

@@ -18,10 +18,13 @@
 # See COPYING file for full licensing terms.
 # See https://www.nexedi.com/licensing for rationale and options.
 
-"""Package xbtree provides utilities for inspecting/manipulating internal structure of BTrees.
+"""Package xbtree provides utilities for inspecting/manipulating internal
+structure of integer-keyed BTrees.
 
 It is primarily used to verify ΔBTail in wcfs.
 
+- `Tree` represents a tree node.
+- `Bucket` represents a bucket node.
 
 XXX Typology:
 """
@@ -97,7 +100,7 @@ def StructureOf(node):
     if is_tree:
         kind, keys, children = bcheck.crack_btree(node, is_map)
         if kind == bcheck.BTREE_EMPTY:
-            return Tree([])
+            return Tree([], Bucket())
 
         if kind == bcheck.BTREE_ONE:
             b = node._bucket_type()

wcfs/internal/xbtree_test.py

@@ -19,15 +19,21 @@
 # See https://www.nexedi.com/licensing for rationale and options.
 
 from wendelin.wcfs.internal import xbtree
+from BTrees.LOBTree import LOBTree
 from BTrees.tests import testBTrees
 
 def test_topologyOf():
     T = xbtree.Tree
     B = xbtree.Bucket
 
-    # XXX empty
+    # empty tree
+    t = LOBTree()
+    assert xbtree.StructureOf(t) == T([], B())
 
-    # XXX 1 k->v
+    # tree with 1 k->v
+    t = LOBTree()
+    t[10] = 'hello'
+    assert xbtree.StructureOf(t) == T([], B(10))
 
     # known degenerate topology, see:
     # https://github.com/zopefoundation/ZODB/commit/6cd24e99f89b
@@ -44,7 +50,7 @@ def test_topologyOf():
                                                 T([], B(7)),
                                                 T([], B(11))) ))
 
-    assert btree.TopoEncodingOf(t) == ((4,), (2,), ø(4), (6,10), ø(5?), ø(7), ø(11), x(5?))
+    #assert btree.TopoEncodingOf(t) == ((4,), (2,), ø(4), (6,10), ø(5?), ø(7), ø(11), x(5?))
 
     """
     assert xbtree.TopologyOf(t) == ( (4,),