Given that the implementation of the .net standard library is provided by the underlined implementation (.Net framework, .Net Core (windows/Linux etc) ). And it is possible that the APIs have little different behaviour. TimeZoneInfo.Id provides different results based on the OS (last time I checked).
So, how to unit test? In visual studio we can either create a .Net Core xUnit project or .Net Framework xUnit project. How to run the same xUnit tests in two different environment?