Add User Testing interface to impl/memory.

service/user/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 user
+
+// Testable is the interface that test implimentations will provide.
+type Testable interface {
+        // SetUser sets the user to a pre-populated User object.
+        SetUser(*User)
+
+        // Login will generate and set a new User object with values derived from
+        // email clientID, and admin values. If clientID is provided, the User will
+        // look like they logged in with OAuth. If it's empty, then this will look
+        // like they logged in via the cookie auth method.
+        Login(email, clientID string, admin bool)
+
+        // Equivalent to SetUser(nil), but a bit more obvious to read in the code :).
+        Logout()
+}