Add testable interface for datastore.

service/datastore/testable.go

Index: service/datastore/testable.go
diff --git a/service/datastore/testable.go b/service/datastore/testable.go
new file mode 100644
index 0000000000000000000000000000000000000000..d1a4e3e6a28888e45271ec81d34c78fa7eba6304
--- /dev/null
+++ b/service/datastore/testable.go
@@ -0,0 +1,35 @@
+// 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.
+	AddIndexes(...*IndexDefinition)

[dnj (Google), 2015/08/14 22:53:54]

Should mention that this an panic if a non-compound index is added. Or maybe it
should return error?

[iannucci, 2015/08/15 01:59:25]

it's for testing, so I'd rather have it panic if the test author does something
stupid.

documented the panic.

+
+	// 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()
+}