public void ContinuousSum_ByAge_SumsAge()
{
var readOnlySource = new ReadOnlyObservableCollection <Person>(_source);
var sumOfAge = readOnlySource.Sum(x => x.Age);
var continuousSum = readOnlySource.ContinuousSum(x => x.Age);
Assert.AreEqual(sumOfAge, continuousSum.CurrentValue);
_source.Add(new Person("Peter", 12));
Assert.AreEqual(sumOfAge + 12, continuousSum.CurrentValue);
}
