checkTransactionalUndoAfterPackWithObjectUnlinkFromRoot(): New method

which tests a particular combination of packing and transactional undo
at the ZODB layer.

src/ZODB/tests/TransactionalUndoStorage.py

@@ -9,12 +9,17 @@ from ZODB import POSException
 from ZODB.Transaction import Transaction
 from ZODB.referencesf import referencesf
 from ZODB.utils import u64
+from ZODB import DB
 
+from Persistence import Persistent
 from ZODB.tests.MinPO import MinPO
 from ZODB.tests.StorageTestBase import zodb_pickle, zodb_unpickle
 
 ZERO = '\0'*8
 
+class C(Persistent):
+    pass
+
 class TransactionalUndoStorage:
 
     def _transaction_begin(self):
@@ -461,3 +466,58 @@ class TransactionalUndoStorage:
         data, revid = self._storage.load(oid, '')
         # The object must now be at the second state
         eq(zodb_unpickle(data), MinPO(52))
+
+    def checkTransactionalUndoAfterPackWithObjectUnlinkFromRoot(self):
+        eq = self.assertEqual
+        db = DB(self._storage)
+        conn = db.open()
+        root = conn.root()
+
+        o1 = C()
+        o2 = C()
+        root['obj'] = o1
+        o1.obj = o2
+        txn = get_transaction()
+        txn.note('o1 -> o2')
+        txn.commit()
+        now = packtime = time.time()
+        while packtime <= now:
+            packtime = time.time()
+
+        o3 = C()
+        o2.obj = o3
+        txn = get_transaction()
+        txn.note('o1 -> o2 -> o3')
+        txn.commit()
+
+        o1.obj = o3
+        txn = get_transaction()
+        txn.note('o1 -> o3')
+        txn.commit()
+
+        log = self._storage.undoLog()
+        eq(len(log), 4)
+        for entry in zip(log, ('o1 -> o3', 'o1 -> o2 -> o3',
+                               'o1 -> o2', 'initial database creation')):
+            eq(entry[0]['description'], entry[1])
+
+        self._storage.pack(packtime, referencesf)
+
+        log = self._storage.undoLog()
+        for entry in zip(log, ('o1 -> o3', 'o1 -> o2 -> o3')):
+            eq(entry[0]['description'], entry[1])
+
+        tid = log[0]['id']
+        db.undo(tid)
+        txn = get_transaction()
+        txn.note('undo')
+        txn.commit()
+        # undo does a txn-undo, but doesn't invalidate
+        conn.sync()
+
+        log = self._storage.undoLog()
+        for entry in zip(log, ('undo', 'o1 -> o3', 'o1 -> o2 -> o3')):
+            eq(entry[0]['description'], entry[1])
+
+        eq(o1.obj, o2)
+        eq(o1.obj.obj, o3)