Have you checked the message log for the errors you are searching for? If you go to Window>Developer Tools>Message Log. When you do, you’ll get this window:
This breaks down what errors you get as you get them and can be used during PIE to see what specifically is occurring. Does this cover what you are looking for? For example, if you run a test that gives you a blatantly null value, the specific instance error should appear when you activate it during PIE, the error will appear in the message log detailing what exactly occurred. In many cases, the specific assets/nodes will be listed and linked, as below:
