Add a simple test for invalidate().

It's harder to write serious tests, because some of the critical
correctness issues relate to concurrency.  We'll have to depend on the
various concurrent updates and NZODBThreads tests to handle these.

src/ZODB/tests/testConnection.py

@@ -335,6 +335,73 @@ class UserMethodTests(unittest.TestCase):
         >>> cn.cacheMinimize(12)
         """
 
+class InvalidationTests(unittest.TestCase):
+
+    # It's harder to write serious tests, because some of the critical
+    # correctness issues relate to concurrency.  We'll have to depend
+    # on the various concurrent updates and NZODBThreads tests to
+    # handle these.
+
+    def test_invalidate(self):
+        r"""
+
+        This test initializes the database with several persistent
+        objects, then manually delivers invalidations and verifies that
+        they have the expected effect.
+
+        >>> db = databaseFromString("<zodb>\n<mappingstorage/>\n</zodb>")
+        >>> cn = db.open()
+        >>> p1 = Persistent()
+        >>> p2 = Persistent()
+        >>> p3 = Persistent()
+        >>> r = cn.root()
+        >>> r.update(dict(p1=p1, p2=p2, p3=p3))
+        >>> get_transaction().commit()
+
+        Transaction ids are 8-byte strings, just like oids; p64() will
+        create one from an int.
+
+        >>> cn.invalidate(p64(1), {p1._p_oid: 1})
+        >>> cn._txn_time
+        '\x00\x00\x00\x00\x00\x00\x00\x01'
+        >>> p1._p_oid in cn._invalidated
+        True
+        >>> p2._p_oid in cn._invalidated
+        False
+        
+        >>> cn.invalidate(p64(10), {p2._p_oid: 1, p64(76): 1})
+        >>> cn._txn_time
+        '\x00\x00\x00\x00\x00\x00\x00\x01'
+        >>> p1._p_oid in cn._invalidated
+        True
+        >>> p2._p_oid in cn._invalidated
+        True
+
+        Calling invalidate() doesn't affect the object state until
+        a transaction boundary.
+        
+        >>> p1._p_state
+        0
+        >>> p2._p_state
+        0
+        >>> p3._p_state
+        0
+
+        The sync() method will abort the current transaction and
+        process any pending invalidations.
+
+        >>> cn.sync()
+        >>> p1._p_state
+        -1
+        >>> p2._p_state
+        -1
+        >>> p3._p_state
+        0
+        >>> cn._invalidated
+        {}
+        
+        """
+
 # ---- stubs
 
 class StubObject(Persistent):