Backend - Implement exchange rate provider for Czech National Bank

.gitignore

@@ -17,6 +17,7 @@
 [Tt]humbs.db
 *.tgz
 *.sublime-*
+.vs/
 
 node_modules
 bower_components

jobs/Backend/ExchangeRateUpdater.Tests/Builders/ExchangeRateBuilderTests.cs

@@ -0,0 +1,147 @@
+using ExchangeRateUpdater.Models;
+using ExchangeRateUpdater.Services.Builders;
+using FluentAssertions;
+
+namespace ExchangeRateUpdater.Tests.Builders;
+
+public class ExchangeRateBuilderTests
+{
+    private readonly ExchangeRateBuilder _builder;
+
+    public ExchangeRateBuilderTests()
+    {
+        _builder = new ExchangeRateBuilder();
+    }
+
+    [Fact]
+    public void BuildExchangeRates_WithMatchingCurrencies_ReturnsCorrectRates()
+    {
+        // Arrange
+        var currencies = new List<Currency>
+        {
+            new Currency("EUR"),
+            new Currency("USD"),
+            new Currency("CZK")
+        };
+
+        var cnbData = new CnbExchangeRateData
+        {
+            Date = DateTime.Now,
+            Rates = new List<CnbExchangeRateEntry>
+            {
+                new CnbExchangeRateEntry { Code = "EUR", Rate = 24.455m, Amount = 1 },
+                new CnbExchangeRateEntry { Code = "USD", Rate = 20.927m, Amount = 1 }
+            }
+        };
+
+        // Act
+        var result = _builder.BuildExchangeRates(currencies, cnbData).ToList();
+
+        // Assert
+        result.Should().HaveCount(2);
+
+        var eurToCzk = result.Single(r => r.SourceCurrency.Code == "EUR");
+        eurToCzk.TargetCurrency.Code.Should().Be("CZK");
+        eurToCzk.Value.Should().Be(24.455m);
+
+        var usdToCzk = result.Single(r => r.SourceCurrency.Code == "USD");
+        usdToCzk.TargetCurrency.Code.Should().Be("CZK");
+        usdToCzk.Value.Should().Be(20.927m);
+    }
+
+    [Fact]
+    public void BuildExchangeRates_WithAmountGreaterThanOne_CalculatesCorrectRate()
+    {
+        var currencies = new List<Currency> { new Currency("JPY"), new Currency("CZK") };
+        var cnbData = new CnbExchangeRateData
+        {
+            Date = DateTime.Now,
+            Rates = new List<CnbExchangeRateEntry>
+            {
+                new CnbExchangeRateEntry
+                {
+                    Code = "JPY",
+                    Rate = 14.165m,
+                    Amount = 100,
+                    Country = "Japan",
+                    Currency = "yen"
+                }
+            }
+        };
+
+        // Act
+        var result = _builder.BuildExchangeRates(currencies, cnbData).ToList();
+
+        // Assert
+        result.Should().HaveCount(1);
+        result[0].Value.Should().Be(0.14165m);
+    }
+
+    [Fact]
+    public void BuildExchangeRates_WithCzkCurrency_ReturnsNoRate()
+    {
+        // Arrange
+        var currencies = new List<Currency> { new Currency("CZK") };
+        var cnbData = new CnbExchangeRateData
+        {
+            Date = DateTime.Now,
+            Rates = new List<CnbExchangeRateEntry>
+            {
+                new CnbExchangeRateEntry { Code = "EUR", Rate = 24.455m, Amount = 1 }
+            }
+        };
+
+        // Act
+        var result = _builder.BuildExchangeRates(currencies, cnbData).ToList();
+
+        // Assert
+        result.Should().BeEmpty();
+    }
+
+    [Fact]
+    public void BuildExchangeRates_WithEmptyCurrencyList_ReturnsEmpty()
+    {
+        // Arrange
+        var currencies = new List<Currency>();
+        var cnbData = new CnbExchangeRateData
+        {
+            Date = DateTime.Now,
+            Rates = new List<CnbExchangeRateEntry>
+            {
+                new CnbExchangeRateEntry { Code = "EUR", Rate = 24.455m, Amount = 1 }
+            }
+        };
+
+        // Act
+        var result = _builder.BuildExchangeRates(currencies, cnbData);
+
+        // Assert
+        result.Should().BeEmpty();
+    }
+
+    [Fact]
+    public void BuildExchangeRates_WithNullCurrencies_ThrowsArgumentNullException()
+    {
+        // Arrange
+        var cnbData = new CnbExchangeRateData
+        {
+            Date = DateTime.Now,
+            Rates = new List<CnbExchangeRateEntry>()
+        };
+
+        // Act & Assert
+        var exception = Assert.Throws<ArgumentNullException>(() => _builder.BuildExchangeRates(null, cnbData).ToList());
+
+        exception.ParamName.Should().Be("source");
+    }
+
+    [Fact]
+    public void BuildExchangeRates_WithNullCnbData_ThrowsNullReferenceException()
+    {
+        // Arrange
+        var currencies = new List<Currency> { new Currency("EUR") };
+
+        // Act & Assert
+        Assert.Throws<NullReferenceException>(() => _builder.BuildExchangeRates(currencies, null).ToList());
+    }
+}