Sometimes I find this useful. This should also help the test errors you mention.

   public class MyTest()
   {
      private readonly IServiceProvider _serviceProvider;
      public MyTest(IServiceProvider serviceProvider)
      {
         _serviceProvider = serviceProvider;
      }

      public void MethodA()
      {
         var serviceA = _serviceProvider.GetService<IServiceA>();
      }

      public void MethodB()
      {
         var serviceB = _serviceProvider.GetService<IServiceB>();
      }
   }