public void GivenDateOfBirth_ShouldCorrectlyCalculateAge()
{
var test = new DateOfBirth("870412");
var beforeBirthday = new DateTime(2017, 4, 2);
Assert.AreEqual(29, test.AgeOn(beforeBirthday));
var onBirthday = new DateTime(2017, 4, 12);
Assert.AreEqual(30, test.AgeOn(onBirthday));
var afterBirthday = new DateTime(2017, 4, 15);
Assert.AreEqual(30, test.AgeOn(afterBirthday));
afterBirthday = new DateTime(2017, 8, 1);
Assert.AreEqual(30, test.AgeOn(afterBirthday));
}