I got this from the new testing template from Google.
Create a new AndroidManifest.xml file in your test or androidTest folder.
<?xml version="1.0" encoding="utf-8"?>
<manifest
xmlns:tools="http://schemas.android.com/tools"
package="your.package.name">
<uses-sdk tools:overrideLibrary="android.support.test.uiautomator.v18"/>
</manifest>