Enhance time zone handling and add unit tests

* Updated the `IZonedTimeInfo` and `ZonedTime` classes to clarify the documentation for the `BaseUtcOffset` property, specifying its relation to UTC.
* Added a new test class `TimeZoneConverterTests` with multiple test methods to verify various functionalities of the `TimeZoneConverter`, including conversions between UTC and time zones, handling of `DateTime` kinds, and mapping to IANA time zones.

Axuno.Tools.Tests/DateAndTime/TimeZoneConverterTests.cs

@@ -0,0 +1,202 @@
+using System.Globalization;
+using NUnit.Framework;
+using NodaTime;
+
+namespace Axuno.Tools.Tests.DateAndTime;
+
+[TestFixture]
+public class TimeZoneConverterTests
+{
+    private static Axuno.Tools.DateAndTime.TimeZoneConverter GetTimeZoneConverter(string culture)
+    {
+        var tzc = new Axuno.Tools.DateAndTime.TimeZoneConverter(
+            new NodaTime.TimeZones.DateTimeZoneCache(NodaTime.TimeZones.TzdbDateTimeZoneSource.Default),
+            "Europe/Berlin",
+            CultureInfo.GetCultureInfo(culture),
+            NodaTime.TimeZones.Resolvers.LenientResolver);
+        return tzc;
+    }
+
+    [Test]
+    public void ConvertUtcToTimeZoneStandard_ShouldReturnCorrectDateTime()
+    {
+        // Arrange
+        var utcDateTime = new DateTime(2022, 1, 1, 12, 0, 0, DateTimeKind.Utc);
+        var expectedDateTime = new DateTime(2022, 1, 1, 13, 0, 0, DateTimeKind.Local);
+
+        // Act
+        var convertedDateTime = GetTimeZoneConverter("de-DE").ToZonedTime(utcDateTime)!;
+
+        // Assert
+        Assert.Multiple(() =>
+        {
+            Assert.That(convertedDateTime.DateTimeOffset.DateTime, Is.EqualTo(expectedDateTime));
+            Assert.That(convertedDateTime.TimeZoneId, Is.EqualTo("Europe/Berlin"));
+            Assert.That(convertedDateTime.CultureInfo.TwoLetterISOLanguageName, Is.EqualTo("de"));
+            Assert.That(convertedDateTime.GenericName, Is.EqualTo("Mitteleuropäische Zeit"));
+            Assert.That(convertedDateTime.GenericAbbreviation, Is.EqualTo("MEZ"));
+            Assert.That(convertedDateTime.DisplayName, Is.EqualTo("(UTC+01:00) Amsterdam, Berlin, Bern, Rom, Stockholm, Wien"));
+            Assert.That(convertedDateTime.Name, Is.EqualTo("Mitteleuropäische Normalzeit"));
+            Assert.That(convertedDateTime.Abbreviation, Is.EqualTo("MEZ"));
+            Assert.That(convertedDateTime.IsDaylightSavingTime, Is.False);
+            Assert.That(convertedDateTime.DateTimeOffset.Offset, Is.EqualTo(new TimeSpan(0, 1, 0, 0)));
+            Assert.That(convertedDateTime.BaseUtcOffset, Is.EqualTo(new TimeSpan(0,1,0,0)));
+        });
+    }
+
+    [Test]
+    public void ConvertUtcToTimeZoneDaylight_ShouldReturnCorrectDateTime()
+    {
+        // Arrange
+        var utcDateTime = new DateTime(2022, 7, 1, 12, 0, 0, DateTimeKind.Utc);
+        var expectedDateTime = new DateTime(2022, 7, 1, 14, 0, 0, DateTimeKind.Local);
+
+        // Act
+        var convertedDateTime = GetTimeZoneConverter("de-DE").ToZonedTime(utcDateTime)!;
+
+        // Assert
+        Assert.Multiple(() =>
+        {
+            Assert.That(convertedDateTime.DateTimeOffset.DateTime, Is.EqualTo(expectedDateTime));
+            Assert.That(convertedDateTime.Name, Is.EqualTo("Mitteleuropäische Sommerzeit"));
+            Assert.That(convertedDateTime.Abbreviation, Is.EqualTo("MESZ"));
+            Assert.That(convertedDateTime.IsDaylightSavingTime, Is.True);
+            Assert.That(convertedDateTime.DateTimeOffset.Offset, Is.EqualTo(new TimeSpan(0, 2, 0, 0)));
+            Assert.That(convertedDateTime.BaseUtcOffset, Is.EqualTo(new TimeSpan(0, 1, 0, 0)));
+        });
+    }
+
+    [Test]
+    public void ConvertUnspecifiedKindToTimeZone_ShouldReturnCorrectDateTime()
+    {
+        // Arrange
+        var unspecifiedDateTime = new DateTime(2022, 1, 1, 12, 0, 0, DateTimeKind.Unspecified);
+        var expectedDateTime = new DateTime(2022, 1, 1, 13, 0, 0, DateTimeKind.Local);
+
+        // Act
+        var convertedDateTime = GetTimeZoneConverter("de-DE").ToZonedTime(unspecifiedDateTime)!;
+
+        // Assert
+        Assert.That(convertedDateTime.DateTimeOffset.DateTime, Is.EqualTo(expectedDateTime));
+    }
+
+    [Test]
+    public void ConvertKindLocalToTimeZone_ShouldReturnCorrectDateTime()
+    {
+        // Arrange
+        var localDateTime = new DateTime(2022, 1, 1, 12, 0, 0, DateTimeKind.Local);
+        var expectedDateTime = new DateTime(2022, 1, 1, 12, 0, 0, DateTimeKind.Local);
+
+        // Act
+        var convertedDateTime = GetTimeZoneConverter("de-DE").ToZonedTime(localDateTime)!;
+
+        // Assert
+        Assert.That(convertedDateTime.DateTimeOffset.DateTime, Is.EqualTo(expectedDateTime));
+    }
+
+    [Test]
+    public void ConvertTimeZoneToUtc_ShouldReturnCorrectDateTime()
+    {
+        // Arrange
+        var localDateTime = new DateTime(2022, 1, 1, 8, 0, 0, DateTimeKind.Local);
+        var expectedDateTime = new DateTime(2022, 1, 1, 7, 0, 0, DateTimeKind.Utc);
+
+        // Act
+        var convertedDateTime = GetTimeZoneConverter("en-US").ToUtc(localDateTime);
+
+        // Assert
+        Assert.That(convertedDateTime, Is.EqualTo(expectedDateTime));
+    }
+
+    [Test]
+    public void ConvertTimeWithZoneIdToUtc_ShouldReturnCorrectDateTime()
+    {
+        // Arrange
+        var localDateTime = new DateTime(2022, 1, 1, 8, 0, 0, DateTimeKind.Local);
+        var expectedDateTime = new DateTime(2022, 1, 1, 7, 0, 0, DateTimeKind.Utc);
+
+        // Act
+        var convertedDateTime = GetTimeZoneConverter("en-US").ToUtc(localDateTime, "Europe/Berlin");
+
+        // Assert
+        Assert.That(convertedDateTime, Is.EqualTo(expectedDateTime));
+    }
+
+    [Test]
+    public void ConvertUtcToTimeZone_ShouldReturnNull_WhenUtcDateTimeIsNull()
+    {
+        // Arrange
+        DateTime? utcDateTime = null;
+
+        // Act
+        var convertedDateTime = GetTimeZoneConverter("de-DE").ToZonedTime(utcDateTime);
+
+        // Assert
+        Assert.That(convertedDateTime, Is.Null);
+    }
+
+    [Test]
+    public void ConvertTimeZoneToUtc_ShouldReturnNull_WhenLocalDateTimeIsNull()
+    {
+        // Arrange
+        DateTime? localDateTime = null;
+
+        // Act
+        var convertedDateTime = GetTimeZoneConverter("en-US").ToUtc(localDateTime);
+
+        // Assert
+        Assert.That(convertedDateTime, Is.Null);
+    }
+
+    [Test]
+    public void ConvertUtcToTimeZone_ShouldReturnNull_WhenDateTimeOfAnyKindIsNull()
+    {
+        // Arrange
+        DateTime? dateTimeOfAnyKind = null;
+
+        // Act
+        var convertedDateTime = GetTimeZoneConverter("en-US").ToZonedTime(dateTimeOfAnyKind);
+
+        // Assert
+        Assert.That(convertedDateTime, Is.Null);
+    }
+
+    [Test]
+    public void ConvertTimeZoneToUtc_ShouldReturnNull_WhenDateTimeOfAnyKindIsNull()
+    {
+        // Arrange
+        DateTime? dateTimeOfAnyKind = null;
+
+        // Act
+        var convertedDateTime = GetTimeZoneConverter("en-US").ToUtc(dateTimeOfAnyKind, "Europe/Berlin");
+
+        // Assert
+        Assert.That(convertedDateTime, Is.Null);
+    }
+    [Test]
+    public void GetTimeZoneList_ShouldReturnTimeZoneList_WhenTimeZoneProviderIsNull()
+    {
+        // Arrange
+        IDateTimeZoneProvider? timeZoneProvider = null;
+
+        // Act
+        var timeZoneList = Axuno.Tools.DateAndTime.TimeZoneConverter.GetTimeZoneList(timeZoneProvider);
+
+        // Assert
+        Assert.That(timeZoneList, Is.InstanceOf<IReadOnlyCollection<string>>());
+    }
+
+    [Test]
+    public void CanMapToIanaTimeZone_ShouldReturnTrue_WhenTimeZoneInfoIsValid()
+    {
+        // Arrange
+        var timeZoneInfo = TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time");
+
+        // Act
+        var canMap = Axuno.Tools.DateAndTime.TimeZoneConverter.CanMapToIanaTimeZone(timeZoneInfo);
+
+        // Assert
+        Assert.That(canMap, Is.True);
+    }
+}
+

Axuno.Tools/DateAndTime/IZonedTimeInfo.cs

@@ -48,7 +48,7 @@ public interface IZonedTimeInfo
     bool IsDaylightSavingTime { get; }
 
     /// <summary>
-    /// Gets the base UTC offset of the timezone related to the <see cref="DateTimeOffset"/>.
+    /// Gets the time difference between the current time zone's standard time and Coordinated Universal Time (UTC).
     /// </summary>
     TimeSpan BaseUtcOffset { get; }
 }

Axuno.Tools/DateAndTime/TimeZoneConverter.cs

@@ -73,7 +73,7 @@ public TimeZoneConverter(IDateTimeZoneProvider dateTimeZoneProvider, string iana
     /// <summary>
     /// Converts the <see cref="DateTime"/> of any <see cref="DateTimeKind"/> to a <see cref="DateTime"/> of <see cref="DateTimeKind.Utc"/>.
     /// </summary>
-    /// <param name="zoneDateTime">A <see cref="DateTime"/> in the the timezone specified with the timezone ID given when creating this converter instance.</param>
+    /// <param name="zoneDateTime">A <see cref="DateTime"/> in the timezone specified with the timezone ID given when creating this converter instance.</param>
     /// <returns>Returns the converted <see cref="DateTime"/> with <see cref="DateTimeKind.Utc"/> or null, if the <paramref name="zoneDateTime"/> parameter is null.</returns>
     public DateTime? ToUtc(DateTime? zoneDateTime)
     {
@@ -83,7 +83,7 @@ public TimeZoneConverter(IDateTimeZoneProvider dateTimeZoneProvider, string iana
     /// <summary>
     /// Converts the <see cref="DateTime"/> of any <see cref="DateTimeKind"/> to a <see cref="DateTime"/> of <see cref="DateTimeKind.Utc"/>.
     /// </summary>
-    /// <param name="zoneDateTime">A <see cref="DateTime"/> in the the timezone specified with the timezone ID given when creating this converter instance.</param>
+    /// <param name="zoneDateTime">A <see cref="DateTime"/> in the timezone specified with the timezone ID given when creating this converter instance.</param>
     /// <returns>Returns the converted <see cref="DateTime"/> with <see cref="DateTimeKind.Utc"/>.</returns>
     public DateTime ToUtc(DateTime zoneDateTime)
     {

Axuno.Tools/DateAndTime/ZonedTime.cs

@@ -57,7 +57,7 @@ internal ZonedTime()
     public bool IsDaylightSavingTime { get; internal set; }
 
     /// <summary>
-    /// Gets the base UTC offset of the timezone related to the <see cref="DateTimeOffset"/>.
+    /// Gets the time difference between the current time zone's standard time and Coordinated Universal Time (UTC).
     /// </summary>
     public TimeSpan BaseUtcOffset { get; internal set; }
 }