dev-test-driven-dev

Write NUnit tests in an EditMode test assembly for pure C# logic like damage calculations or state machines. Use the Unity Test Framework with [TestFixture] and [Test] attributes, and place tests in a Tests/EditMode folder with its own .asmdef file.

EditMode tests run fast without a scene and suit pure logic, math, and state machines. PlayMode tests run in a live scene and are required for MonoBehaviour lifecycle behavior, physics, collisions, and time-based logic using [UnityTest] with coroutines.

Use Substitute.For<IInterface>() to create a mock of the dependency interface, inject it into the system under test, and simulate events with Raise.Event<Action>(). This isolates logic from scene dependencies without manual stub classes.

Use PlayMode tests when verifying MonoBehaviour lifecycle methods like Awake and Start, physics interactions, UI event bindings, or anything requiring a live GameObject. EditMode tests cannot instantiate scene-dependent behavior reliably.

Read the assertion error message precisely, trace the failure to the exact line, and fix the production implementation. Never weaken or modify the test to make it pass, then re-run until all tests are green.