JSON is bundled up with the Android SDK, so you’ll just be hitting a stub. You can pull in a JSON jar, which will provide real objects to use.
To do this, you’ll need to add this to your build.gradle:
testImplementation 'org.json:json:20140107'
Alternatively, you can download and include the jar.
testCompile files('libs/json.jar')
Note that the latest version of JSON is built for Java 8, so you’ll need to grab 20140107
You may also need to clean and rebuild the project.