Add the ability to disable special automatic entities in impl/memory

service/datastore/testable.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package datastore
 
 // TestingSnapshot is an opaque implementation-defined snapshot type.
 type TestingSnapshot interface {
         ImATestingSnapshot()
 }
@@ skipping 39 matching lines @@
         // CatchupIndexes or use Take/SetIndexSnapshot to manipulate the index state.
         Consistent(always bool)
 
         // AutoIndex controls the index creation behavior. If it is set to true, then
         // any time the datastore encounters a missing index, it will silently create
         // one and allow the query to succeed. If it's false, then the query will
         // return an error describing the index which could be added with AddIndexes.
         //
         // By default this is false.
         AutoIndex(bool)
+
+        // DisableSpecialEntities turns off maintenance of special __entity_group__
+        // type entities. By default this mainenance is enabled, but it can be
+        // disabled by calling this with true.
+        //
+        // If it's true:
+        //   - AllocateIDs returns an error.
+        //   - Put'ing incomplete Keys returns an error.
+        //   - Transactions are disabled and will return an error.
+        //
+        // This is mainly only useful when using an embedded in-memory datastore as
+        // a fully-consistent 'datastore-lite'. In particular, this is useful for the
+        // txnBuf filter which uses it to fulfil queries in a buffered transaction,
+        // but never wants the in-memory versions of these entities to bleed through
+        // to the user code.
+        DisableSpecialEntities(bool)
 }