Mock Collision Object in Unity

Question

Problem:

I'm trying to set up some tests with mock collision objects, but i cannot construct collisions with custom objects. What I'm trying to do:

Collision2D col = new Collision2D();
col.gameObject = this.gameObject;

There seems to be no way to do this as col.gameObject has no visible setter. Is there a way to do this? I would like to script the passing of a collision to a mono-behavior via an event that gets handled by the OnCollisionEnter2D(Collision2D collision) inherited from mono-behaviors. Thanks for your time.

Answer 1

This looks like a job for reflection:

public T MockType<T>(Dictionary<string,object> fieldValues, params object[] consParams)
{
    var type = typeof (T);
    var cons = type.GetConstructor(BindingFlags.NonPublic,
                                   Type.DefaultBinder,
                                   consParams.Select(p => p.GetType()).ToArray(),
                                   null);
    var result = (T)cons.Invoke(consParams ?? new object[0]); // invoke non-public constructor
    foreach (var fieldValue in fieldValues)
    {
        var field = type.GetField(fieldValue.Key, BindingFlags.NonPublic)
        field.SetValue(result, fieldValue.Value); // Set non-public field
    }
    return result;
}


// Example method demonstrating use:
public Collision2D MockCollision2D(Rigidbody2D rigidbody,
                                   Collider2D collider,
                                   Vector2 relativeVelocity,
                                   ContactPoint2D[] contacts)
{
    return MockType<Collision2D>(new Dictionary<string, object>
                                     {
// Use a decompiler like ILSpy to find out what the internal fields' names are:
                                         {"m_Rigidbody", rigidbody},
                                         {"m_Collider", collider},
                                         {"m_RelativeVelocity", relativeVelocity},
                                         {"m_Contacts", contacts}
                                     },
                                 new object[0]
        );
}

I haven't tested this, so it might need some tweaks. The game object the collision refers to is drawn from the collider field.

Answer 2

Do not new MonoBehaviour just add them as components. Your approach won't work.

EDIT: I still advise you against breaking the component and Monobehaviour approach. If you want testing then have a look at the Unity Testing Tools. They will provide you with everything you need including mocks and stubs for unit and integration tests.

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