Add emulation of transaction retries to memory impl of RunInTransaction.

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
 
 type TestingSnapshot interface{}
 
 // Testable is the testable interface for fake datastore implementations.
 type Testable interface {
@@ skipping 15 matching lines @@
         SetIndexSnapshot(TestingSnapshot)
 
         // CatchupIndexes catches the index table up to the current state of the
         // datastore. This is equivalent to:
         //   idxSnap := TakeIndexSnapshot()
         //   SetIndexSnapshot(idxSnap)
         //
         // But depending on the implementation it may implemented with an atomic
         // operation.
         CatchupIndexes()
+
+        // SetTransactionRetryCount set how many times RunInTransaction will retry
+        // transaction body pretending transaction conflicts happens. 0 (default)
+        // means commit succeeds on the first attempt (no retries).
+        SetTransactionRetryCount(int)
 }