public void GetManagersBudget_ReturnsBudget(string managerId, long expected)
        {
            List <Employee> employees = new List <Employee>
            {
                Employee.Create("Employee1", "", 1000),
                Employee.Create("Employee2", "Employee1", 800),
                Employee.Create("Employee3", "Employee1", 500),
                Employee.Create("Employee4", "Employee2", 500),
                Employee.Create("Employee6", "Employee2", 500),
                Employee.Create("Employee5", "Employee1", 500)
            };
            EmployeesServices services = new EmployeesServices(employees);
            var result = services.GetManagersBudget(managerId);

            Assert.Equal(expected, result);
        }
        public void GetManagersBudget_ThrowsArgumentNullException_WhenIdIsInvalid(string managerId)
        {
            EmployeesServices services = new EmployeesServices(new List <Employee>());

            Assert.Throws <ArgumentNullException>(nameof(managerId), () => services.GetManagersBudget(managerId));
        }