Testing the Sad Path

When_passing_null_measurements.cs

using NUnit.Framework;

namespace Domain.Tests.AveragingCalculator_Tests.SadPath
{
[Category("AveragingCalculator")]
public class When_passing_null_measurements
{

private AveragingCalculator _averageCalculator;

[SetUp]
public void Setup()
{
_averageCalculator = new AveragingCalculator();
}

[Test]
[ExpectedException(typeof(ArgumentNullException))]
public void When_measurement_is_null()
{
var measurements = Mother.Get4Measurements();
measurements.Add(null);

_averageCalculator.Aggregate(measurements);
}
}

AveragingCalculator.cs

namespace Domain
{
public class AveragingCalculator : IAggregateCalculator
{
if(measurements.Contains(null))
{
throw new ArgumentNullException();
}

return new Measurement()
{
HighValue=measurements.Average(m=>m.HighValue),
LowValue=measurements.Average(m=>m.LowValue)
};

}