public void TestGetByEmailNull()
        {
            Administrator administrator = new Administrator()
            {
                Id       = 1,
                Email    = "*****@*****.**",
                Password = "******"
            };
            List <Administrator> administrators = new List <Administrator>()
            {
                administrator,
                new Administrator()
                {
                    Id       = 2,
                    Email    = "*****@*****.**",
                    Password = "******"
                },
            };

            administrators.ForEach(s => _context.Add(s));
            _context.SaveChanges();
            var repository = new AdministratorRepository(_context);

            var result = repository.GetByEmail("*****@*****.**");

            Assert.IsNull(result);
        }