unity-testability

To make MonoBehaviour code testable, isolate pure logic that does not depend on Transform or GameObject scene state into plain C# classes, leaving only thin wiring and input translation in the MonoBehaviour.

Use EditMode tests in Unity for pure C# logic without scene dependencies, and PlayMode tests for behavior that requires GameObject or scene context. Separate pure logic from MonoBehaviour to run reliable EditMode tests without fragile scene setups.

The best way to isolate Unity-facing code for dependency injection is to design seams and interfaces around scene interactions. Inject interfaces for engine dependencies to mock interactions and test pure C# modules independently of the Unity scene context.

You do not need to extract all MonoBehaviour logic into pure C# for unit testing. Avoid unnecessary abstraction for tiny, scene-bound scripts and preserve Unity-facing responsibilities like scene binding to prevent over-engineering your project architecture.

Unity PlayMode tests are fragile when core logic is tightly coupled to scene state. Fix them by moving algorithms into testable pure C# modules, reserving PlayMode tests strictly for scene-dependent behavior and dependency-injected seams.