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

impl/memory/context.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 memory
 
 import (
         "errors"
         "sync"
 
@@ skipping 117 matching lines @@
 //
 // It really should have been appengine.Context.RunInTransaction(func(tc...)),
 // but because it's not, this method is on dsImpl instead to mirror the official
 // API.
 //
 // The fake implementation also differs from the real implementation because the
 // fake TaskQueue is NOT backed by the fake Datastore. This is done to make the
 // test-access API for TaskQueue better (instead of trying to reconstitute the
 // state of the task queue from a bunch of datastore accesses).
 func (d *dsImpl) RunInTransaction(f func(context.Context) error, o *ds.TransactionOptions) error {
+        if d.data.getDisableSpecialEntities() {
+                return errors.New("special entities are disabled. no transactions for you")
+        }
+
         // Keep in separate function for defers.
         loopBody := func(applyForReal bool) error {
                 curMC := cur(d.c)
 
                 txnMC := curMC.mkTxn(o)
 
                 defer func() {
                         txnMC.Lock()
                         defer txnMC.Unlock()
 
@@ skipping 20 matching lines @@
         if o != nil && o.Attempts != 0 {
                 attempts = o.Attempts
         }
         for attempt := 0; attempt < attempts; attempt++ {
                 if err := loopBody(attempt >= d.data.txnFakeRetry); err != ds.ErrConcurrentTransaction {
                         return err
                 }
         }
         return ds.ErrConcurrentTransaction
 }