public void WhenCalling_CalculateInvoice_WithValidDataI()
{
SKUModel sKUModel = new SKUModel();
sKUModel.QuatityOfA = 3;
sKUModel.QuatityOfB = 5;
sKUModel.QuatityOfC = 1;
sKUModel.QuatityOfD = 1;
var result = promotionEngineObj.CalculateInvoice(sKUModel);
Assert.AreEqual(result, 280);
}