Add testable interface for datastore.

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 {
+        // AddIndex adds the provided index.
+        // Blocks all datastore access while the index is built.
+        // Panics if any of the IndexDefinition objects are not Compound()
+        AddIndexes(...*IndexDefinition)
+
+        // TakeIndexSnapshot allows you to take a snapshot of the current index
+        // tables, which can be used later with SetIndexSnapshot.
+        TakeIndexSnapshot() TestingSnapshot
+
+        // SetIndexSnapshot allows you to set the state of the current index tables.
+        // Note that this would allow you to create 'non-lienarities' in the precieved
+        // index results (e.g. you could force the indexes to go back in time).
+        //
+        // SetIndexSnapshot takes a reference of the given TestingSnapshot. You're
+        // still responsible for closing the snapshot after this call.
+        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()
+}