It is time to implement all the classes from the preceding class diagram and look at our overall source and project structure.

Let's open Visual Studio and create a blank solution named EmployeeBeneftis.sln. In this solution, let's add a project of the Class Library type named Domain.

We will now add all the classes to the Domain project. In order to minimize the compilation errors, we will start with the class that does not refer to other classes. Right-click on the Domain project in Visual Studio and add a class named Address. Use the following code for the body of the class:

namespace Domain
{
  public class Address
  {
    public string AddressLine1 { get; set; }
    public string AddressLine2 { get; set; }
    public string Postcode { get; set; }
    public string City { get; set; }
    public string Country { get; set; }
  }
}

Let's add a second class named Benefit and use the following code snippet: This class acts as a base class for any class that represents an employee benefit:

namespace Domain
{
  public class Benefit
  {
    public string Name { get; set; }
    public string Description { get; set; }
    public Employee Employee { get; set; }
  }
}

Next, we can add classes representing our three benefits. Before this, let's define the enumeration that will be used by the leave benefit as follows:

namespace Domain
{
  public enum LeaveType
  {
    Casual,
    Sick,
    Unpaid
  }
}

With the enumeration in place, here is the code snippet for our three employee benefit classes:

namespace Domain
{
  public class SkillsEnhancementAllowance : Benefit
  {
    public int RemainingEntitlement { get; set; }
    public int Entitlement { get; set; }
  }
}


namespace Domain
{
  public class SeasonTicketLoan : Benefit
  {
    public int Amount { get; set; }
    public double MonthlyInstalment { get; set; }
    public DateTime StartDate { get; set; }
    public DateTime EndDate { get; set; }
  }
}

namespace Domain
{
  public class Leave : Benefit
  {
    public LeaveType Type { get; set; }
    public int AvailableEntitlement { get; set; }
    public int RemainingEntitlement { get; set; }
  }
}

We have all the classes in place except the class that represents an employee. Let's add one more classes named Employee and use the following code snippet:

namespace Domain
{
  public class Employee
  {
    public string EmployeeNumber { get; set; }
    public string Firstname { get; set; }
    public string Lastname { get; set; }
    public string EmailAddress { get; set; }
    public DateTime DateOfBirth { get; set; }
    public DateTime DateOfJoining { get; set; }

    public Address ResidentialAddress { get; set; }
    public bool IsAdmin { get; set; }
    public string Password { get; set; }
    public ICollection<Benefit> Benefits { get; set; }
  }
}

Note that we have a collection of Benefit classes in the Employee class. Not every employee may be eligible for every type of benefit. So, we cannot have an association to every benefit type in Employee. A collection of benefits helps with such a situation when you do not know in advance which benefits a particular employee is eligible for. Our code should compile at this point. If not, just fix whatever errors come up.

Next, we are going to add one more project for our unit tests. So, let's add another project of the Class Library type and name it Tests.Unit. This project needs to reference the Domain project because we will be calling into the classes defined in the Domain project from our tests. We are going to use NUnit to write our tests. So, let's go and grab NUnit by using NuGet.

using NUnit.Framework

namespace Tests.Unit
{
  [TestFixture]
  public class EmployeeTests
  {
    [Test]
    public void EmployeeIsEntitledToPaidLeaves()
    {
      //Arrange
      var employee = new Employee();

      //Act
      employee.Leaves = new List<Leave>();
      employee.Leaves.Add(new Leave
      {
        Type = LeaveType.Paid,
        AvailableEntitlement = 15
      });

      //Assert
      var paidLeave = employee.Leaves.FirstOrDefault(l => l.Type == LeaveType.Paid);
      Assert.That(paidLeave, Is.Not.Null);
      Assert.That(paidLeave.AvailableEntitlement, Is.EqualTo(15));
    }
  }
}