The main reason for this migration is the lack of availability of a reliable NUnit alternative in NuGet for .NET Core.
For documentation on the differences between NUnit and XUnit, please check out this document in github
Just include the right XUnit dependency and dotnet test will automatically figure out how to run your tests.
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFramework>netcoreapp2.2</TargetFramework>
<IsPackable>false</IsPackable>
</PropertyGroup>
<ItemGroup>
<PackageReference Include="FluentAssertions" Version="5.5.3" />
<PackageReference Include="Microsoft.AspNetCore.TestHost" Version="2.2.0" />
<PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.9.0" />
<PackageReference Include="Moq" Version="4.10.1" />
<PackageReference Include="xunit" Version="2.4.0" />
<PackageReference Include="xunit.runner.visualstudio" Version="2.4.0" />
</ItemGroup>
<ItemGroup>
<ProjectReference Include="..\..\src\Namespace.Namespace.Foo\Namespace.Namespace.Foo.csproj" />
</ItemGroup>
</Project>
The other really important thing to note is that the project reference here takes a relative path, whereas with the preview2 tooling, you could get away with just specifying the name of the project directory.