The interface for the Employee Manager class looks like this:

    namespace Applications.BusinessLogic.Managers
    {
        public interface IEmployeeManager : IBusinessManager
        {
          int GetTotalNumberOfEmployees();


          /// <summary>
          /// Adds the new employee into the DB
          /// </summary>
          /// <returns></returns>
          Employee AddNewEmployee(Employee newEmployee);

          void RemoveAnEmployee(Employee newEmployee);

           /// <summary>
          /// Gets the List of All Employees eventually 
          from data source
          /// </summary>
          /// <returns></returns>
          IEnumerable<Employee> GetListofAllEmployees();

          Employee GetAnEmployee(int employeeId);
        }
    }

Let's look at the implementation code, which is as written as follows:

    public class EmployeeManager : IEmployeeManager
    {
        private IRepository _employeeRepository;
        protected readonly Employee DEFAULT_EMPLOYEE;

        public EmployeeManager(IRepository 
        employeeRepository) : base()
        {
            _employeeRepository = employeeRepository;
            DEFAULT_EMPLOYEE = new Employee { FirstName = 
            "Not found", FamilyName = "Not found", Employee_ID = 0 };
        }

        public int GetTotalNumberOfEmployees()
        {
            return _employeeRepository.GetRecordsCount<Employee>();
        }

        public Employee AddNewEmployee(Employee newEmployee)
        {
            _employeeRepository.Create(newEmployee);
            return newEmployee;
        }

        public IEnumerable<Employee> GetListofAllEmployees()
        {
            return _employeeRepository.GetAll<Employee>();
        }

        public void RemoveAnEmployee(Employee newEmployee)
        {
            _employeeRepository.Delete(newEmployee);
        }

        public Employee GetAnEmployee(int employeeId)
        {
            var employee = _employeeRepository.GetEntity<Employee>
            (employeeId);
            if (employee == null) return DEFAULT_EMPLOYEE;
            return employee;
        }
    }