private static List <ServiceDescriptor> ConfigureServices() { var descriptors = new List <ServiceDescriptor>(); var services = Substitute.For <IServiceCollection>(); services.When(s => s.Add(Arg.Any <ServiceDescriptor>())) .Do(args => descriptors.Add(args[0] as ServiceDescriptor)); var logger = Substitute.For <ILogger>(); var configure = new Singletons(); configure.Logger = logger; configure.ConfigureServices(services); return(descriptors); }