Importing Nuget/External library to Unity, which built target to use?

So I'm new to developing with C# and Unity and trying to get testing workflow done in Unity.

I plan to use the internal Unity test runner as testing framework and NSubstitute as mocking tool. I also know that Unity version that have Scripting runtime 4.x equivalent supports .Net 4.x and netstandard 2.0 compatible library from an article on Microsoft Docs (link)

This may seem as a stupid question to ask, but what does that support for .Net 4.x and netstandard 2.0 in API compatibility level means when we imported the external DLLs?

Do I need to copy the .dll from a package that targets netstandard 2.0 if I use that same API compatibility level in the setting or can I also use net45 or net46 build with that same choice of API compatibility level?

Any help or insight is much appreciated.

 

What are the results of your testing, are you receiving an error?