Coin Changer kata with Reduce in C# using MS Tests

CoinChangerTests.cs

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

namespace CoinChanger
{
    [TestClass]
    public class CoinChangerTests
    {
        [TestMethod]
        [ExpectedException(typeof(ApplicationException))]
        public void GivenNoCoins_WhenInvokedWith0_ItMustThrowAnApplicationException()
        {
            var target = new CoinChanger();

            target.ChangeFor(0);
        }

        [TestMethod]
        public void GivenPennies_WhenInvokedWith0_ItMustReturn0Pennies()
        {
            var target = new CoinChanger { Coins = new[] { 1 } };

            var actual = target.ChangeFor(0);

            var expected = new[] { 0 };
            CollectionAssert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void GivenPennies_WhenInvokedWith1_ItMustReturn1Penny()
        {
            var target = new CoinChanger { Coins = new[] { 1 } };

            var actual = target.ChangeFor(1);

            var expected = new[] { 1 };
            CollectionAssert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void GivenPennies_WhenInvokedWith3_ItMustReturn3Pennies()
        {
            var target = new CoinChanger { Coins = new[] { 1 } };

            var actual = target.ChangeFor(3);

            var expected = new[] { 3 };
            CollectionAssert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void GivenNickels_WhenInvokedWith5_ItMustReturn1Nickel()
        {
            var target = new CoinChanger { Coins = new[] { 5 } };

            var actual = target.ChangeFor(5);

            var expected = new[] { 1 };
            CollectionAssert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void GivenNickelsAndPennies_WhenInvokedWith6_ItMustReturn1NickelAnd1Penny()
        {
            var target = new CoinChanger { Coins = new[] { 5, 1 } };

            var actual = target.ChangeFor(6);

            var expected = new[] { 1, 1 };
            CollectionAssert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void GivenNickelsAndPennies_WhenInvokedWith9_ItMustReturn1NickelAnd4Pennies()
        {
            var target = new CoinChanger { Coins = new[] { 5, 1 } };

            var actual = target.ChangeFor(9);

            var expected = new[] { 1, 4 };
            CollectionAssert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void GivenDimesNickelsAndPennies_WhenInvokedWith19_ItMustReturn1Dime1NickelAnd4Pennies()
        {
            var target = new CoinChanger { Coins = new[] { 10, 5, 1 } };

            var actual = target.ChangeFor(19);

            var expected = new[] { 1, 1, 4 };
            CollectionAssert.AreEqual(expected, actual);
        }

        [TestMethod]
        public void GivenQuartersDimesNickelsAndPennies_WhenInvokedWith99_ItMustReturn3Quarters2Dime0NickelsAnd4Pennies()
        {
            var target = new CoinChanger { Coins = new[] { 25, 10, 5, 1 } };

            var actual = target.ChangeFor(99);

            var expected = new[] { 3, 2, 0, 4 };
            CollectionAssert.AreEqual(expected, actual);
        }
    }

    public class CoinChanger
    {
        public int[] Coins { get; set; }

        public int[] ChangeFor(int amount)
        {
            if (Coins == null) throw new ApplicationException("Must have some coins before being called.");

            return Coins.Aggregate(
                new Working
                {
                    Change = new List<int>(),
                    Amount = amount
                },
                (m, coin) =>
                {
                    m.Change.Add(m.Amount / coin);
                    m.Amount %= coin;
                    return m;
                }).Change.ToArray();

        }

        class Working
        {
            public IList<int> Change { get; set; }
            public int Amount { get; set; }
        }
    }
}