public void ToRomanNumerals()
{
RomanNumerals.FromInteger(1).Should().Be("I");
RomanNumerals.FromInteger(2).Should().Be("II");
RomanNumerals.FromInteger(3).Should().Be("III");
RomanNumerals.FromInteger(4).Should().Be("IV");
RomanNumerals.FromInteger(5).Should().Be("V");
RomanNumerals.FromInteger(1981).Should().Be("MCMLXXXI");
}