Add Subtract impl + tests

Source/Singulink.Globalization.Currency/SortedMoneySet.cs

@@ -299,6 +299,28 @@ public void SetAmount(decimal amount, Currency currency)
         _amountLookup[currency] = amount;
     }
 
+    /// <summary>
+    /// Subtracts the specified value from this set. Zero amounts are not trimmed from the set.
+    /// </summary>
+    /// <remarks>
+    /// Default values that are not associated with any currency are ignored.
+    /// </remarks>
+    public void Subtract(Money value) => Add(-value);
+
+    /// <summary>
+    /// Subtracts the specified currency and amount from this set.
+    /// </summary>
+    public void Subtract(decimal amount, string currencyCode) => Add(-amount, currencyCode);
+
+    /// <summary>
+    /// Adds the specified currency and amount to this set.
+    /// </summary>
+    public void Subtract(decimal amount, Currency currency)
+    {
+        EnsureCurrencyAllowed(currency, nameof(currency));
+        AddInternal(amount, currency);
+    }
+
     /// <summary>
     /// Copies the values in this set to a new immutable set that uses the same registry as this set.
     /// </summary>

Tests/Singulink.Globalization.Currency.Tests/SortedMoneySetTests/SubtractTests.cs

@@ -0,0 +1,124 @@
+using Shouldly;
+
+namespace Singulink.Globalization.Tests.SortedMoneySetTests;
+
+[TestClass]
+public class SubtractTests
+{
+    private static readonly Money Usd100 = new(100m, "USD");
+    private static readonly Money Cad50 = new(50m, "CAD");
+    private static readonly Money Eur25 = new(25m, "EUR");
+    private static readonly Money Aud75 = new(75m, "AUD");
+    private static readonly ImmutableSortedMoneySet ImmutableSet = [Usd100, Cad50, Eur25];
+
+    private readonly SortedMoneySet _set = ImmutableSet.ToSet();
+
+    // public void Subtract(Money value) tests
+
+    [TestMethod]
+    public void Money_CurrencyExists_SubtractsPositiveAmountAndReturnsPositiveAmount()
+    {
+        _set.Subtract(Usd100);
+        _set.Count.ShouldBe(3);
+        _set.ShouldBe([new(0m, "USD"), Cad50, Eur25]);
+    }
+
+    [TestMethod]
+    public void MoneyCurrencyExists_SubtractsZeroAmountAndReturnsPositiveAmount()
+    {
+        _set.Subtract(new(-0m, "EUR"));
+        _set.Count.ShouldBe(3);
+        _set.ShouldBe([Usd100, Cad50, Eur25]);
+    }
+
+    [TestMethod]
+    public void MoneyCurrencyNotInSet_AddsValueToSet()
+    {
+        _set.Subtract(-Aud75);
+        _set.ShouldBe([Usd100, Cad50, Eur25, Aud75]);
+    }
+
+    [TestMethod]
+    public void MoneyCurrencyDisallowed_ThrowsArgumentException()
+    {
+        var value = new Money(100, new Currency("Blah blah blah", "BBB", "$$", 2));
+
+        Should.Throw<ArgumentException>(() => _set.Subtract(value))
+            .Message.ShouldBe($"The currency '{value.Currency}' is not present in the set's currency registry. (Parameter 'value')");
+
+        _set.Count.ShouldBe(3);
+        _set.ShouldBe([Usd100, Cad50, Eur25]);
+    }
+
+    // public void Subtract(decimal amount, string currencyCode) tests
+
+    [TestMethod]
+    public void CurrencyCodeExists_SubtractsPositiveAmountAndReturnsPositiveAmount()
+    {
+        _set.Subtract(100m, "USD");
+        _set.Count.ShouldBe(3);
+        _set.ShouldBe([new(0m, "USD"), Cad50, Eur25]);
+    }
+
+    [TestMethod]
+    public void CurrencyCodeExists_SubtractsZeroAmountAndReturnsPositiveAmount()
+    {
+        _set.Subtract(-0m, "EUR");
+        _set.Count.ShouldBe(3);
+        _set.ShouldBe([Usd100, Cad50, Eur25]);
+    }
+
+    [TestMethod]
+    public void CurrencyCodeNotInSet_AddsValueToSet()
+    {
+        _set.Subtract(-75m, "AUD");
+        _set.ShouldBe([Usd100, Cad50, Eur25, Aud75]);
+    }
+
+    [TestMethod]
+    public void CurrencyCodeDisallowed_ThrowsArgumentException()
+    {
+        Should.Throw<ArgumentException>(() => _set.Subtract(100m, "Blah blah blah"))
+            .Message.ShouldBe("Currency code 'Blah blah blah' not found in the 'System' registry. (Parameter 'currencyCode')");
+
+        _set.Count.ShouldBe(3);
+        _set.ShouldBe([Usd100, Cad50, Eur25]);
+    }
+
+    // public void Subtract(decimal amount, Currency currency) tests
+
+    [TestMethod]
+    public void CurrencyExists_SubtractsPositiveAmountAndReturnsPositiveAmount()
+    {
+        _set.Subtract(-100m, Currency.Get("USD"));
+        _set.Count.ShouldBe(3);
+        _set.ShouldBe([new(0m, "USD"), Cad50, Eur25]);
+    }
+
+    [TestMethod]
+    public void CurrencyExists_SubtractsZeroAmountAndReturnsPositiveAmount()
+    {
+        _set.Subtract(-0m, Currency.Get("EUR"));
+        _set.Count.ShouldBe(3);
+        _set.ShouldBe([Usd100, Cad50, Eur25]);
+    }
+
+    [TestMethod]
+    public void CurrencyNotInSet_AddsValueToSet()
+    {
+        _set.Subtract(75m, Currency.Get("AUD"));
+        _set.ShouldBe([Usd100, Cad50, Eur25, Aud75]);
+    }
+
+    [TestMethod]
+    public void CurrencyDisallowed_ThrowsArgumentException()
+    {
+        var disallowedCurrency = new Currency("XXX", "Non-existent currency", "X", 2);
+
+        Should.Throw<ArgumentException>(() => _set.Subtract(100m, disallowedCurrency))
+            .Message.ShouldBe($"The currency '{disallowedCurrency}' is not present in the set's currency registry. (Parameter 'currency')");
+
+        _set.Count.ShouldBe(3);
+        _set.ShouldBe([Usd100, Cad50, Eur25]);
+    }
+}