title: App.config not loading into dotnet core nunit project
body: <p>I have a testing project that I'm running on netcore 3.0, referencing a framework library. The library uses <code>ConfigurationManager</code> to access app settings from App.config. I have an App.config in the root of the testing library and it's compiling into the bin/Debug/netcoreapp3.0 folder without a problem; I can see a file called Tests.dll.config there. However, it's not loading into the project, and when I try calling <code>Configuration.AppSettings.AllKeys</code> I get nothing.</p>
  
  <p>I've been trying to do some research but the only solution that is being suggested is to ensure that there is an App.config file in the root of the test project (see <a href="https://stackoverflow.com/a/516245">here</a>). I do have this file, it's compiling fine, but it's not getting used. What can be the problem?</p>