One of the key ideas of the Nullable Infrastructure is that all the semantics of the infrastructure class remain exactly the same other than disabling external

One of the key ideas of the Nullable Infrastructure is that all the semantics of the infrastructure class remain exactly the same other than disabling external communication. So any logic inside the infrastructure code still runs. This is important because we don't have broad integration tests. That's why the null code is inside the infrastructure, instead of using the classic Null Object pattern. It's also a major difference between it and classic test doubles. And perhaps your simulators?