public void WithTransportSerializer_should_replace_existing_registration_when_input_null() { var services = new ServiceCollection(); var sagaTypeResolver = NSubstitute.Substitute.For <ISagaTypeResolver>(); var typeResolver = NSubstitute.Substitute.For <ITypeResolver>(); var sysInfo = SystemInfo.New(); var sut = new BusConfigurator(services, sagaTypeResolver, typeResolver, sysInfo); sut.WithTransportSerializer <FakeTransportSerializer>(); var sp = services.BuildServiceProvider(); var serializer = sp.GetService <ITransportSerializer>(); serializer.Should().NotBeNull() .And.BeOfType <FakeTransportSerializer>(); }