Tests.cs

public class Tests
{
    [Fact]
    public void Shipment_IsLate_Returns_True_When_Past_Date()
    {
        var shipment = new Shipment
        {
            DeliveryDate = DateTime.Today.AddDays(-1)
        };
        var policy = new StandardDeliveryTiming(DateTime.Today);

        Assert.True(shipment.IsLate(policy));
    }
    
    [Fact]
    public void Shipment_IsLate_Returns_False_When_Not_Past_Date_With_Buffer()
    {
        var shipment = new Shipment
        {
            DeliveryDate = DateTime.UtcNow.AddMinutes(-15)
        };
        var policy = new BufferDeliveryTiming(DateTime.UtcNow, TimeSpan.FromMinutes(30));

        Assert.False(shipment.IsLate(policy));
    }
}