migrate usage of StringBuilder+TagBuilder for HTML rendering

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Related to How to migrate usage of StringBuilder+TagBuilder for HTML rendering?

Extensions.cs

namespace AspNetCoreTests;

using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Mvc.Rendering;
using System;
using System.Text;
using System.Text.Encodings.Web;

public static class Extensions
{
    public static void AppendEx(this StringBuilder builder, IHtmlContent? content)
    {
        if (content != null)
        {
            using (var writer = new StringWriter(builder))
            {
                content.WriteTo(writer, HtmlEncoder.Default);
            }
        }
    }

    public static void AppendEx(this StringBuilder contents, IHtmlContentBuilder html)
    {
        // why do we need to do that? my StringBuilder is no good enough?
        using (var writer = new StringWriter(contents))
        {
            html.WriteTo(writer, HtmlEncoder.Default);
        }
    }

    public static void AppendEx(this StringBuilder contents, TagBuilder tag)
    {
        // why do we need to do that? my StringBuilder is no good enough?
        using (var writer = new StringWriter(contents))
        {
            tag.WriteTo(writer, HtmlEncoder.Default);
        }
    }

    public static void SetInnerText(this TagBuilder tag, string value)
    {
        tag.InnerHtml.Append(value);
    }

    public static void Append(this StringWriter writer, IHtmlContent html)
    {
        html.WriteTo(writer, HtmlEncoder.Default);
    }

    public static IHtmlContent ToString(this TagBuilder tag, TagRenderMode mode)
    {
        if (mode == TagRenderMode.StartTag)
        {
            return tag.RenderStartTag();
        }
        else if (mode == TagRenderMode.EndTag)
        {
            return tag.RenderEndTag();
        }
        else
        {
            throw new ArgumentException();
        }
    }
}

TagBuilderHowTos.cs

namespace UnitTests;

using AspNetCoreTests;
using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.Extensions.Primitives;
using System.Text;
using System.Text.Encodings.Web;

public class TagBuilderHowTos
{
#if NETFRAMEWORK || false
    /// <summary>
    /// The old way.
    /// </summary>
    [Fact]
    public void Test0()
    {
        var contents = new StringBuilder();
        var tag = new TagBuilder("div");
        tag.SetInnerText("hello");
    
        contents.Append(tag.ToString(TagRenderMode.StartTag));
        Assert.Equal("<div>", contents.ToString());

        contents.Append(tag.InnerHtml);
        Assert.Equal("<div>hello", contents.ToString());

        contents.Append(tag.ToString(TagRenderMode.EndTag));
        Assert.Equal("<div>hello</div>", contents.ToString());

        var result = MvcHtmlString.Create(contents.ToString());
        Assert.Equal("<div>hello</div>", result.ToString());
    }
#endif

#if NETCOREAPP
    /// <summary>
    /// Set RenderMode and use extension methods.
    /// </summary>
    /// <remarks>So many StringWriters</remarks>
    [Fact]
    public void Test1()
    {
        var contents = new StringBuilder();
        var tag = new TagBuilder("div");
        tag.InnerHtml.Append("hello");
        
        tag.TagRenderMode = TagRenderMode.StartTag;
        contents.AppendEx(tag);
        Assert.Equal("<div>", contents.ToString());

        contents.AppendEx(tag.InnerHtml);
        Assert.Equal("<div>hello", contents.ToString());

        tag.TagRenderMode = TagRenderMode.EndTag;
        contents.AppendEx(tag);
        Assert.Equal("<div>hello</div>", contents.ToString());

        var result = new HtmlString(contents.ToString());
        Assert.Equal("<div>hello</div>", result.ToString());
    }

    /// <summary>
    /// Use Render methods and use extension methods.
    /// </summary>
    /// <remarks>So many StringWriters</remarks>
    [Fact]
    public void Test2()
    {
        var contents = new StringBuilder();
        var tag = new TagBuilder("div");
        tag.InnerHtml.Append("hello");
        
        contents.AppendEx(tag.RenderStartTag());
        Assert.Equal("<div>", contents.ToString());

        contents.AppendEx(tag.RenderBody());
        Assert.Equal("<div>hello", contents.ToString());

        contents.AppendEx(tag.RenderEndTag());
        Assert.Equal("<div>hello</div>", contents.ToString());

        var result = new HtmlString(contents.ToString());
        Assert.Equal("<div>hello</div>", result.ToString());
    }

    /// <summary>
    /// Use StringWriter instead of StringBuilder.
    /// </summary>
    /// <remarks>No more StringBuilder</remarks>
    [Fact]
    public void Test3()
    {
        var contents = new StringWriter();
        var tag = new TagBuilder("div");
        tag.InnerHtml.Append("hello");

        tag.RenderStartTag().WriteTo(contents, HtmlEncoder.Default);
        Assert.Equal("<div>", contents.ToString());

        tag.RenderBody()?.WriteTo(contents, HtmlEncoder.Default);
        Assert.Equal("<div>hello", contents.ToString());

        tag.RenderEndTag().WriteTo(contents, HtmlEncoder.Default);
        Assert.Equal("<div>hello</div>", contents.ToString());

        var result = new HtmlString(contents.ToString());
        Assert.Equal("<div>hello</div>", result.ToString());
    }

    /// <summary>
    /// Minimal code changes: extension methods.
    /// </summary>
    [Fact]
    public void Test4()
    {
        var contents = new StringWriter(); // change this type
        var tag = new TagBuilder("div");
        tag.SetInnerText("hello"); // 1 extension method

        contents.Append(tag.ToString(TagRenderMode.StartTag)); // 2 extension methods
        Assert.Equal("<div>", contents.ToString());

        contents.Append(tag.InnerHtml); // 1 extension method
        Assert.Equal("<div>hello", contents.ToString());

        contents.Append(tag.ToString(TagRenderMode.EndTag)); // 2 extension methods
        Assert.Equal("<div>hello</div>", contents.ToString());

        var result = new HtmlString(contents.ToString());
        Assert.Equal("<div>hello</div>", result.ToString());
    }
#endif
}