Try using ` com.google.appengine:appengine-testing` utilities

[armiol]

Currently we don't use any of the test helpers that exist for AppEngine.

However, we may benefit from some of them. For instance, there are some tools to emulate the eventual consistency without having to configure the datastore emulator manually. See this article for some of examples.

[armiol]

@dmdashenkov @yuri-sergiichuk FYI.

[yuri-sergiichuk]

@armiol AFAIK those test classes work only with AppEngine APIs (ones from com.google.appengine.api package), while we are using GCloud APIs (com.google.cloud).