Resolved Mock RaycastHit2D

I'm trying to cover my code with tests, especially code that deals with raycasts and raycasts hits as I constantly face issues with small miscalculations. It's really tiresome to create gameObjects and colliders, set them in specific positions, layers, sizes, and call `Physics2D.Raycast()` everytime I need to test If my code is correctly handling `RaycastHit2D` structs.

For some reason, when `RaycastHit2D` is created manually (using new `RaycastHit2D()`) I cannot set a collider property on it.

I've tried to use reflection to set this property using code I found on stackOverflow

I've looked at decompiled source code of Unity here, but unfortunately the `m_Collider` type is `int32` not `Collider2D` (I'm using Unity ver. `2019.4.17f1`).

Then I looked at UntiyCsReference and I found that inside `RaycastHit2D`, `m_Collider` is defined as an integer which seems to be instanceID of the collider.
I've tried to set `m_Collider` on `RaycastHit2D` to `instanceID` of Collider2D but when I run the code `hit.collider` is still returning null. I also checked that after I set private field using Reflection from linked stack-overflow response, I get 0 when I use the same code to get private field value.


1. Are there any reasons why developer cannot set `collider` property during creation of this `RaycastHit2D`?
2. Is there any way I could mock `RaycastHit2D` using reflection or any other means?

Solved

As it turned out I was passing copy of `RaycastHit2D` to the function that was responsible for setting a private field, and returning unchanged original struct. That's why `m_Collider` was always set to 0. After changing the code to this:

Code (CSharp):

1.  
2.     public static RaycastHit2D MockHit(Collider2D collider, Vector2 point, Vector2 normal, float distance) {
3.       RaycastHit2D hit = new RaycastHit2D() {
4.         point = point,
5.         normal = normal,
6.         distance = distance
7.       };
8.       object obj = hit;
9.       Type type = obj.GetType();
10.       FieldInfo fieldInfo = type.GetField("m_Collider", BindingFlags.NonPublic | BindingFlags.Instance);
11.       fieldInfo.SetValue(obj, collider.GetInstanceID());
12.       return (RaycastHit2D)obj;
13.     }
14.  
15.  

I return `obj` casted to RaycastHit2D which make it work. Previously I was returning `hit` unaware that `obj` is a copy.