Example of a solution to the Roman Numerals Kata, done Craftsmanship Grenoble

Roman-spec.ts

import {assert} from "chai";
import {Roman} from "../src/Roman";

function toRoman(arabic: number) {
  return new Roman().toRoman(arabic);
}

describe('RomanNumbers', () => {
  describe('toRoman() is', () => {

    function assertRomanIs(arabic: number, expected: string) {
      assert.equal(toRoman(arabic), expected);
    }

    it('I for 1', () => {
      assertRomanIs(1, 'I');
    });

    it('II for 2', () => {
      assertRomanIs(2, 'II');
    });

    it('is III for 3', () => {
      assertRomanIs(3, 'III');
    });

    it('is IV for 4', () => {
      assertRomanIs(4, 'IV');
    });

    it('adds V for numbers between 8 and 5', () => {
      assertRomanIs(5, 'V')
      assertRomanIs(6, 'VI');
      assertRomanIs(7, 'VII');
      assertRomanIs(8, 'VIII');
    });

    it('is IX for 9', () => {
      assertRomanIs(9, 'IX');
    });

    it('adds X for numbers between 19 and 10', () => {
      assertRomanIs(10, 'X');
      assertRomanIs(11, 'XI');
      // ...
    });

  });
});

RomanNumerals.ts

export class Roman {

  public toRoman(numberToConvert: number) {

    let romanDigits: [number, string][] = [
      [10, 'X'],
      [9, 'IX'],
      [5, 'V'],
      [4, 'IV'],
      [1, 'I'],
    ];

    let romanNumber = "";
    romanDigits.forEach(([arabic, romanDigit]) => {
      while (numberToConvert >= arabic) {
        romanNumber += romanDigit;
        numberToConvert -= arabic;
      }
    });
    return romanNumber;
  }
}