EnumDescriptionConverterTests.cs

using Xunit;

using CommunityToolkit.Maui.Converters;

using System.ComponentModel;
using System.ComponentModel.DataAnnotations;

namespace CommunityToolkit.Maui.UnitTests.Converters;

public class EnumDescriptionConverterTests : BaseOneWayConverterTest<EnumDescriptionConverter>
{
   enum TestEnum
	{
		[Display(Name = "Display Name")]
		WithDisplay,
		[Description("Description Text")]
		WithDescription,
		NoAttribute
	}

	enum MultiAttributeEnum
	{
		[Display(Name = "Display Name")]
		[Description("Description Text")]
		Both,
		[Display(Name = "")]
		[Description("Description Text")]
		EmptyDisplay,
		[Display(Name = " ")]
		[Description("Description Text")]
		WhitespaceDisplay,
		[Description("")]
		EmptyDescription,
	}

  [Fact]
  public void ConvertFrom_ThrowsArgumentNullException_WhenNull()
  {
	var converter = (ICommunityToolkitValueConverter)new EnumDescriptionConverter();
	Assert.Throws<ArgumentNullException>(() => converter.Convert(null, typeof(string), null, null));
  }

	[Fact]
	public void ConvertFrom_FallbackToValueToString_WhenInvalidEnumValue()
	{
		var converter = new EnumDescriptionConverter();
		// Cast an int not defined in MultiAttributeEnum
		var invalid = (MultiAttributeEnum)999;
		var result = converter.ConvertFrom(invalid);
		Assert.Equal("999", result);
	}

	[Fact]
	public void ConvertFrom_ReturnsDisplayName()
	{
		var converter = new EnumDescriptionConverter();
		var result = converter.ConvertFrom(TestEnum.WithDisplay);
		Assert.Equal("Display Name", result);
	}

	[Fact]
	public void ConvertFrom_ReturnsDescriptionText()
	{
		var converter = new EnumDescriptionConverter();
		var result = converter.ConvertFrom(TestEnum.WithDescription);
		Assert.Equal("Description Text", result);
	}

	[Fact]
	public void ConvertFrom_ReturnsEnumName_WhenNoAttribute()
	{
		var converter = new EnumDescriptionConverter();
		var result = converter.ConvertFrom(TestEnum.NoAttribute);
		Assert.Equal("NoAttribute", result);
	}


  [Fact]
	public void ConvertFrom_DisplayTakesPrecedence_WhenBothAttributes()
	{
		var converter = new EnumDescriptionConverter();
		var result = converter.ConvertFrom(MultiAttributeEnum.Both);
		Assert.Equal("Display Name", result);
	}

	[Fact]
	public void ConvertFrom_FallbackToDescription_WhenDisplayEmpty()
	{
		var converter = new EnumDescriptionConverter();
		var result = converter.ConvertFrom(MultiAttributeEnum.EmptyDisplay);
		Assert.Equal("Description Text", result);
	}

	[Fact]
	public void ConvertFrom_FallbackToDescription_WhenDisplayWhitespace()
	{
		var converter = new EnumDescriptionConverter();
		var result = converter.ConvertFrom(MultiAttributeEnum.WhitespaceDisplay);
		Assert.Equal("Description Text", result);
	}

	[Fact]
	public void ConvertFrom_FallbackToEnumName_WhenDescriptionEmpty()
	{
		var converter = new EnumDescriptionConverter();
		var result = converter.ConvertFrom(MultiAttributeEnum.EmptyDescription);
		Assert.Equal("EmptyDescription", result);
	}

	#region DisplayAttribute Localization & Edge Cases

	public class TestResources
	{
		public static string LocalizedDisplay => "Localized Display";
		public static int NonStringResource => 42;
	}

	enum LocalizedEnum
	{
		[Display(Name = "LocalizedDisplay", ResourceType = typeof(TestResources))]
		Localized,
		[Display(Name = "MissingResource", ResourceType = typeof(TestResources))]
		MissingResource,
		[Display(Name = null)]
		NullName,
		[Display(Name = " ")]
		WhitespaceName,
		[Display(Name = "NonStringResource", ResourceType = typeof(TestResources))]
		NonStringResource,
	}

	[Fact]
	public void ConvertFrom_ReturnsLocalizedDisplay_WhenResourceTypeSet()
	{
		var converter = new EnumDescriptionConverter();
		var result = converter.ConvertFrom(LocalizedEnum.Localized);
		Assert.Equal("Localized Display", result);
	}

	[Fact]
	public void ConvertFrom_FallbackToName_WhenResourceMissing()
	{
		var converter = new EnumDescriptionConverter();
		var result = converter.ConvertFrom(LocalizedEnum.MissingResource);
		Assert.Equal("MissingResource", result);
	}

	[Fact]
	public void ConvertFrom_FallbackToEnumName_WhenDisplayNameNull()
	{
		var converter = new EnumDescriptionConverter();
		var result = converter.ConvertFrom(LocalizedEnum.NullName);
		Assert.Equal("NullName", result);
	}

	[Fact]
	public void ConvertFrom_FallbackToEnumName_WhenDisplayNameWhitespace()
	{
		var converter = new EnumDescriptionConverter();
		var result = converter.ConvertFrom(LocalizedEnum.WhitespaceName);
		Assert.Equal("WhitespaceName", result);
	}

	[Fact]
	public void ConvertFrom_FallbackToEnumName_WhenGetNameThrows()
	{
		var converter = new EnumDescriptionConverter();
		var result = converter.ConvertFrom(LocalizedEnum.NonStringResource);
		Assert.Equal("NonStringResource", result);
	}

	#endregion

	#region DescriptionAttribute Edge Cases

	enum DescriptionEdgeEnum
	{
		[Description("")]
		EmptyDescription,
	}

	[Fact]
	public void ConvertFrom_FallbackToEnumName_WhenDescriptionEmptyEdge()
	{
		var converter = new EnumDescriptionConverter();
		var result = converter.ConvertFrom(DescriptionEdgeEnum.EmptyDescription);
		Assert.Equal("EmptyDescription", result);
	}

	#endregion
}