public void IfTooLongOrWhitespace()
        {
            var veryLong = "very long";

            Assert.Throws <DesignByContractViolationException>(
                () => Fail.IfTooLongOrWhitespace(veryLong, 3, nameof(veryLong))
                );

            Assert.Throws <DesignByContractViolationException>(
                () => Fail.IfTooLongOrWhitespace(null, 3, nameof(veryLong))
                );

            Assert.Throws <DesignByContractViolationException>(
                () => Fail.IfTooLongOrWhitespace(" ", 3, nameof(veryLong))
                );

            Fail.IfTooLongOrWhitespace("a ", 2, "a ");
            Fail.IfTooLongOrWhitespace("aa", 300, "aa");
            Fail.IfTooLongOrWhitespace("aa", 2, "aa");
        }