Add unit tests for AbpSelectTagHelperService info text rendering

- Verify info text is rendered as <div class="form-text"> (not <small>)
- Verify aria-describedby is set on the select tag

framework/test/Volo.Abp.AspNetCore.Mvc.UI.Tests/Volo/Abp/AspNetCore/Mvc/UI/Bootstrap/TagHelpers/Form/AbpSelectTagHelperService_Tests.cs

@@ -0,0 +1,129 @@
+#nullable enable
+
+using System.Collections.Generic;
+using System.Reflection;
+using System.Text.Encodings.Web;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc.ModelBinding;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using Microsoft.Extensions.Localization;
+using Shouldly;
+using Xunit;
+
+namespace Volo.Abp.AspNetCore.Mvc.UI.Bootstrap.TagHelpers.Form;
+
+public class AbpSelectTagHelperService_Tests
+{
+    [Fact]
+    public async Task Info_text_should_be_rendered_as_div_with_form_text_class()
+    {
+        var service = new TestAbpSelectTagHelperService();
+        var tagHelper = new AbpSelectTagHelper(service)
+        {
+            AspFor = CreateModelExpression(),
+            InfoText = "Description"
+        };
+
+        var output = CreateOutput();
+
+        await tagHelper.ProcessAsync(CreateContext(), output);
+
+        service.LastGroupHtml.ShouldContain("<div class=\"form-text\"");
+        service.LastGroupHtml.ShouldContain("id=\"TestSelectInfoText\"");
+        service.LastGroupHtml.ShouldNotContain("<small");
+    }
+
+    [Fact]
+    public async Task Info_text_should_set_aria_describedby_on_select()
+    {
+        var service = new TestAbpSelectTagHelperService();
+        var tagHelper = new AbpSelectTagHelper(service)
+        {
+            AspFor = CreateModelExpression(),
+            InfoText = "Description"
+        };
+
+        var output = CreateOutput();
+
+        await tagHelper.ProcessAsync(CreateContext(), output);
+
+        service.LastSelectTag.ShouldNotBeNull();
+        service.LastSelectTag!.Attributes.ContainsName("aria-describedby").ShouldBeTrue();
+        service.LastSelectTag.Attributes["aria-describedby"].Value.ToString().ShouldBe("TestSelectInfoText");
+    }
+
+    private static TagHelperContext CreateContext()
+    {
+        return new TagHelperContext(
+            new TagHelperAttributeList(),
+            new Dictionary<object, object>(),
+            "test");
+    }
+
+    private static TagHelperOutput CreateOutput()
+    {
+        return new TagHelperOutput(
+            "abp-select",
+            new TagHelperAttributeList(),
+            (_, _) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+    }
+
+    private static ModelExpression CreateModelExpression()
+    {
+        var metadataProvider = new EmptyModelMetadataProvider();
+        return new ModelExpression(
+            "TestSelect",
+            metadataProvider.GetModelExplorerForType(typeof(string), null));
+    }
+
+    private sealed class TestAbpSelectTagHelperService : AbpSelectTagHelperService
+    {
+        public string LastGroupHtml { get; private set; } = string.Empty;
+
+        public TagHelperOutput? LastSelectTag { get; private set; }
+
+        public TestAbpSelectTagHelperService()
+            : base(null!, HtmlEncoder.Default, new FakeTagHelperLocalizer(), null!, null!)
+        {
+        }
+
+        protected override Task<TagHelperOutput> GetSelectTagAsync(TagHelperContext context, TagHelperOutput output, TagHelperContent childContent)
+        {
+            LastSelectTag = new TagHelperOutput(
+                "select",
+                new TagHelperAttributeList { { "id", "TestSelect" } },
+                (_, _) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()))
+            {
+                TagMode = TagMode.StartTagAndEndTag
+            };
+
+            return Task.FromResult(LastSelectTag);
+        }
+
+        protected override Task<string> GetLabelAsHtmlAsync(TagHelperContext context, TagHelperOutput output, TagHelperOutput selectTag)
+        {
+            return Task.FromResult(string.Empty);
+        }
+
+        protected override Task<string> GetValidationAsHtmlAsync(TagHelperContext context, TagHelperOutput output, TagHelperOutput selectTag)
+        {
+            return Task.FromResult(string.Empty);
+        }
+
+        protected override void AddGroupToFormGroupContents(TagHelperContext context, string propertyName, string html, int order, out bool suppress)
+        {
+            LastGroupHtml = html;
+            suppress = false;
+        }
+    }
+
+    private sealed class FakeTagHelperLocalizer : IAbpTagHelperLocalizer
+    {
+        public string GetLocalizedText(string text, ModelExplorer explorer) => text;
+
+        public IStringLocalizer? GetLocalizerOrNull(ModelExplorer explorer) => null;
+
+        public IStringLocalizer? GetLocalizerOrNull(Assembly assembly) => null;
+    }
+}