public void AddRequirement_ValidRequirementAndExpectedProcessingTimeSet()
{
// Arrange
const VisaType type = VisaType.D;
var visa = new Visa(type);
var requirementName = RequirementName.FromString("Invitation Letter");
var requirementDescription =
RequirementDescription.FromString("A letter of acceptance from a foreign university.");
var requirementExample = RequirementExample.FromString("acceptance_letter_example.png");
visa.SetExpectedProcessingTime(VisaExpectedProcessingTime.FromInt(30));
// Act
visa.AddRequirement(requirementName, requirementDescription, requirementExample);
//Assert
Assert.NotEmpty(visa.Requirements);
}