shim.PropertyBSet = s=>{};
another way of doing is in the constructor
ShimClassA.Constructor =(@this)=>
{
var shim = new Shimclass(@this){PropertyBSet=s=>{};};
}
I am not sure, if you would get any benefit out of this. I would still advise to shim the getter of the PropertyB to return whatever you like.
ShimClass.AllInstances.PropertyBGet =()=>{return something;};