MainActivity_Tests.cs

  public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsApplicationActivity
  {
      protected override void OnCreate(Bundle savedInstanceState)
      {
          base.OnCreate(savedInstanceState);

          global::Xamarin.Forms.Forms.Init(this, savedInstanceState);

          // This will load all tests within the current project
          var nunit = new NUnit.Runner.App();

          // If you want to add tests in another assembly
          //nunit.AddTestAssembly(typeof(MyTests).Assembly);

          // Do you want to automatically run tests when the app starts?
          nunit.AutoRun = true;

          LoadApplication(nunit);
      }
  }