Your friend Joyce from another country wants you to have a video call at 20.**.2017 12:00. Will you join?
Whether you are writing your own unit tests or reviewing ones written by someone else, you can easily assess their quality by the shape of the test methods. You don't even need to read them.
Imagine yourself riding a bicycle where all the screw-nuts are loosened. Everything is rattling and the bike is ready to fall apart. This is exactly how it feels to maintain code when this essential keyword we are going to discuss is not used or is used only sparingly for some class fields and constants.
The short answer is both. Let me explain.