Roman Numeral kata with Reduce in C# using MS Tests

RomanNumeralTests.cs

using System.Collections.Generic;
using System.Linq;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace RomanNumerals
{
    [TestClass]
    public class RomanNumeralTests
    {
        [TestMethod]
        public void Given0_WhenRomanizeIsInvoke_ItMustReturnAnEmptyString()
        {
            var target = new Numerals();

            var actual = target.Romanize(0);

            var expected = string.Empty;
            Assert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void Given1_WhenRomanizeIsInvoke_ItMustReturnI()
        {
            var target = new Numerals();

            var actual = target.Romanize(1);

            const string expected = "I";
            Assert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void Given2_WhenRomanizeIsInvoke_ItMustReturnII()
        {
            var target = new Numerals();

            var actual = target.Romanize(2);

            const string expected = "II";
            Assert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void Given3_WhenRomanizeIsInvoke_ItMustReturnIII()
        {
            var target = new Numerals();

            var actual = target.Romanize(3);

            const string expected = "III";
            Assert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void Given4_WhenRomanizeIsInvoke_ItMustReturnIV()
        {
            var target = new Numerals();

            var actual = target.Romanize(4);

            const string expected = "IV";
            Assert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void Given5_WhenRomanizeIsInvoke_ItMustReturnV()
        {
            var target = new Numerals();

            var actual = target.Romanize(5);

            const string expected = "V";
            Assert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void Given6_WhenRomanizeIsInvoke_ItMustReturnVI()
        {
            var target = new Numerals();

            var actual = target.Romanize(6);

            const string expected = "VI";
            Assert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void Given7_WhenRomanizeIsInvoke_ItMustReturnVII()
        {
            var target = new Numerals();

            var actual = target.Romanize(7);

            const string expected = "VII";
            Assert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void Given9_WhenRomanizeIsInvoke_ItMustReturnIX()
        {
            var target = new Numerals();

            var actual = target.Romanize(9);

            const string expected = "IX";
            Assert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void Given10_WhenRomanizeIsInvoke_ItMustReturnX()
        {
            var target = new Numerals();

            var actual = target.Romanize(10);

            const string expected = "X";
            Assert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void Given29_WhenRomanizeIsInvoke_ItMustReturnXXIX()
        {
            var target = new Numerals();

            var actual = target.Romanize(29);

            const string expected = "XXIX";
            Assert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void Given30_WhenRomanizeIsInvoke_ItMustReturnXXX()
        {
            var target = new Numerals();

            var actual = target.Romanize(30);

            const string expected = "XXX";
            Assert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void Given89_WhenRomanizeIsInvoke_ItMustReturnLXXXIX()
        {
            var target = new Numerals();

            var actual = target.Romanize(89);

            const string expected = "LXXXIX";
            Assert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void Given49_WhenRomanizeIsInvoke_ItMustReturnXLIX()
        {
            var target = new Numerals();

            var actual = target.Romanize(49);

            const string expected = "XLIX";
            Assert.AreEqual(expected, actual);
        }
    }

    public class Numerals
    {
        private readonly Dictionary<int, string> _lookup;

        public Numerals()
        {
            _lookup = new Dictionary<int, string>
            {
                {50, "L"}, {40, "XL"},
                {10, "X"}, { 9, "IX"},
                { 5, "V"}, { 4, "IV"},
                { 1, "I"}
            };
        }

        public string Romanize(int value)
        {
            return _lookup.Aggregate(string.Empty, (m, l) =>
            {
                while (value >= l.Key)
                {
                    m += l.Value;
                    value -= l.Key;
                }

                return m;
            });
        }
    }
}