Add testable interface for datastore.

service/datastore/interface.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
 
 import (
         "golang.org/x/net/context"
 )
 
@@ skipping 122 matching lines @@
         // resolved keys back to the items in src.
         PutMulti(src interface{}) error
 
         // DeleteMulti removes items from the datastore.
         DeleteMulti(keys []Key) error
 
         // Raw returns the underlying RawInterface. The Interface and RawInterface may
         // be used interchangably; there's no danger of interleaving access to the
         // datastore via the two.
         Raw() RawInterface
+
+        // Testable returns the Testable interface for the implementation, or nil if
+        // there is none.
+        Testable() Testable

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

Since most implementations return nil here, should this really be a
datastore.Interface method? It feels like it's bloating the interface.

I think that "Testable" and all supporting functions should be moved into
impl/memory, since:
(a) it's the only thing that's going to implement Testable, and
(b) different implementations down the road may have different controls or
testable primitives.

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

There's no way to cast to it, which is why I'm doing this in the first place.
memory doesn't have the necessary access to the types to get a Testable from a
RawInterface.

I've moved this down to RawInterface only

[dnj (Google), 2015/08/15 02:07:53]

I was thinking something like:

testable := memory.Testable(ctx)

func Testable(ctx context.Context) {
  d := ds.getUnfiltered(ctx)
  //          ^ make me public
  if d != nil {
    if t, ok := d.(*dsImpl); ok {
      return t
    }
  }
}

 }