The start of a test mixin for storages with pack(). This isn't

complete or correct yet (Jim, feel free to start filing it in! :)

src/ZODB/tests/PackableStorage.py

+# Run some tests relevant for storages that support pack()
+
+try:
+    import cPickle
+    pickle = cPickle
+    #import cPickle as pickle
+except ImportError:
+    import pickle
+
+try:
+    from cStringIO import StringIO
+except ImportError:
+    from StringIO import StringIO
+
+import time
+
+from ZODB.referencesf import referencesf
+from Persistence import Persistent
+
+
+
+class Object:
+    def __init__(self, oid):
+        self._oid = oid
+
+    def getoid(self):
+        return self._oid
+
+
+
+class PackableStorage:
+    def _newobj(self):
+        if not hasattr(self, '_cache'):
+            self._cache = {}
+        obj = Object(self._storage.new_oid())
+        self._cache[obj.getoid()] = obj
+        return obj
+
+    # Override StorageTestBase's method, since we're generating the pickles
+    # in this class explicitly.
+    def _massagedata(self, data):
+        return data
+
+    def checkOldRevisionPacked(self):
+        # The initial revision has an object graph like so:
+        # o1 -> o2 -> o3
+        o1 = self._newobj()
+        o2 = self._newobj()
+        o3 = self._newobj()
+        o1.object = o2
+        o2.object = o3
+        # Pickle these objects
+        def dumps(obj):
+            def getpersid(obj):
+                return obj.getoid()
+            s = StringIO()
+            p = pickle.Pickler(s)
+            p.persistent_id = getpersid
+            p.dump(obj)
+            return s.getvalue()
+        p1, p2, p3 = map(dumps, (o1, o2, o3))
+        # Now commit these objects
+        revid1 = self._dostore(oid=o1.getoid(), data=p1)
+        revid2 = self._dostore(oid=o2.getoid(), data=p2)
+        revid3 = self._dostore(oid=o3.getoid(), data=p3)
+        # Record this moment in history so we can pack everything before it
+        t0 = time.time()
+        # Now change the object graph to look like so:
+        # o1 -> o3
+        # and note that o2 is no longer referenced
+        o1.object = o3
+        revid11 = self._dostore(oid=o1.getoid(), revid=revid1, data=dumps(o1))
+        # Pack away transaction 2
+        self._storage.pack(t0, referencesf)
+        # Now, objects 1 and 3 should exist, but object 2 should have been
+        # reference counted away.  First, we need a custom unpickler.
+        def loads(str, persfunc=self._cache.get):
+            fp = StringIO(str)
+            u = pickle.Unpickler(fp)
+            u.persistent_load = persfunc
+            return u.load()
+        # Get object 1
+        data, revid = self._storage.load(o1.getoid(), '')
+        assert revid == revid11
+        from ZODB import utils
+        assert loads(loads(data)).getoid() == o1.getoid()
+        # Get object 3
+        data, revid = self._storage.load(o3.getoid(), '')
+        assert revid == revid2
+        assert loads(loads(data)).getoid() == o3.getoid()
+        # Object 2 should fail
+        self.assertRaises(KeyError,
+                          self._storage.load, o2.getoid(), '')