It's a good idea to write as much of the logic for a game as isolated, non-Monobehavior classes, that are easy to unit test in Edit mode. However, some of the logic in a game relates to things that happen when the game is running. Examples include physics, collisions, and timing-based events. We test these parts of our games in Play Mode.
In this recipe, we'll create one very simple Play Mode test, to check that physics affects a RigidBody (based on an example from the Unity documentation):
![](https://static.packt-cdn.com/products/9781788471909/graphics/assets/7d7fe717-66e1-4c2b-bbdb-6b312ea5e15f.png)