public void CompareTo_ReturnsExpectedSign(string postalCodeBefore, string postalCodeAfter)
{
var b = new DZPostalCode(postalCodeBefore);
var a = new DZPostalCode(postalCodeAfter);
Assert.AreEqual(Math.Sign(-1), Math.Sign(b.CompareTo(a)));
Assert.AreEqual(Math.Sign(1), Math.Sign(a.CompareTo(b)));
}