Testing a Component's Startup

Unity Engine
1

I have a component I want to unit test. I wrote two unit tests, they get run and fail. Debugging them seems to show that adding the component to a game object does not trigger the component’s Start() method (where the logic I’m testing is). How do I test my Start() method (making Start() public and calling it manually is not an option)?

This is my component:

public class CameraAspectRatioLockScr : MonoBehaviour
{
    public Camera ParentCamera { get; private set; }

    void Start ()
    {
        this.ParentCamera = this.gameObject.GetComponentInParent<Camera>();

        if (this.ParentCamera == null)
        {
            throw new MissingComponentException("CameraAspectRatioLockScr failed to find a Camera component in its parent.");
        }
    }
}

These are my unit tests

namespace UnityTest
{
    [TestFixture]
    public class CameraAspectRatioLockTests
    {
        private GameObject SetUpCamera()
        {
            var parentCamera = new GameObject();
            parentCamera.AddComponent<Camera>();

            return parentCamera;
        }

        [Test]
        public void ComponentFindsParentCamera()
        {
            var parentCamera = this.SetUpCamera();

            var subject = parentCamera.AddComponent<CameraAspectRatioLockScr>();

            Assert.IsNotNull(subject.ParentCamera);
        }

        [Test]
        public void ComponentThrowsExceptionWhenParentCameraNotFound()
        {
            var parentObject = new GameObject();

            Assert.Throws<MissingComponentException> (()=>parentObject.AddComponent<CameraAspectRatioLockScr>());
        }
    }
}
2

I think start will not get called until the next frame, while you are testing on this frame. Try awake or onenable.

3

Hmm… I tried it and neither OnEnable nor Awake help. I wouldn’t imagine frames would have anything to do with component instantiation, would they?

Can I somehow trigger Unity to poke the Start() method? Is there a specific method I can call to make Unity initialize the component?

4

You can just make it public and call it yourself directly if you want- the “special functions” are found and added to a list in the background using reflection and it apparently ignores the accessibility of the function.

More importantly, I don’t see where you’re actually making anything a parent of anything else. Am I blind and missing it? GetComponentInParent isn’t actually going to return anything with no parent.

5

Awake should be called before the next line of code is run after AddComponent.

Start will not be called until immediately before a components first frame. So you would need to make your unit test a coroutine and wait one frame before checking the assertion.

As a general note calls to GetComponent normally belong in Awake instead of Start.

Alternatively you could call Start yourself using reflection. This strikes me as messy.

Lack of a decent unit testing framework is considered a draw back of Unity by many.

6

I tried awake already and don’t want to make Start public. My temporary solution is to add a protected class inside my unit test file that inherits from my component that has a method void Start that calls base.Start(). That seems to work and shouldn’t pollute my solution with too many classes. The unit test solution I’ll sacrifice to class-pollution I guess :smile: