public void SVNoDebePoderRetorarUnDeDoctor()
        {
            string id   = null;
            var    data = new List <Doctor>
            {
                new Doctor {
                    Codigo        = "jfuert", Apellidos = "Coral", Celular = "11111",
                    IdDoctor      = "ssssss", Nombres = "Anderson", NumeroDocumento = "4783434",
                    TipoDocumento = TipoDocumento.DNI
                },

                new Doctor {
                    Apellidos       = "GOMEZ MACEDO", Celular = "11111",
                    IdDoctor        = "ddddd", Nombres = "JAVIER ANGEL",
                    NumeroDocumento = "4783434", TipoDocumento = TipoDocumento.DNI
                }
            }.AsQueryable();

            var dbset = new Mock <DbSet <Doctor> >();

            dbset.As <IQueryable <Doctor> >().Setup(m => m.Provider).Returns(data.Provider);
            dbset.As <IQueryable <Doctor> >().Setup(m => m.Expression).Returns(data.Expression);
            dbset.As <IQueryable <Doctor> >().Setup(m => m.ElementType).Returns(data.ElementType);
            dbset.As <IQueryable <Doctor> >().Setup(m => m.GetEnumerator()).Returns(data.GetEnumerator());

            var context = new Mock <OpticaContext>();

            context.Setup(a => a.Doctores).Returns(dbset.Object);

            var service = new DoctorService(context.Object);

            var doctor = service.DoctorModificar(id);

            Assert.IsNull(doctor);
        }