Firstly, this isn’t a bug, or something that you might have done wrong; it’s intentional. Essentially, you can’t run a .Net Standard Library, so your tests aren’t runnable.
Okay - so I want to convert to .Net Core 3.0!
Yep - that’s exactly what you want, and it’s this easy; open up the csproj file - it’ll look like this:
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFramework>netstandard2.0</TargetFramework>
</PropertyGroup>
And replace it with this:
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFramework>netcoreapp3.0</TargetFramework>
</PropertyGroup>
And that’s it - your tests should now run!