Custom `Microsoft.VisualStudio.TestTools.WebTesting.ExtractionRule` that groups all of the form field `Microsoft.VisualStudio.TestTools.WebTesting.HtmlTag`s for ASP.NET MVC-style view model array form field names.

ExtractArrayFields.cs

using System;
using System.Collections.Generic;
using Microsoft.VisualStudio.TestTools.WebTesting;

namespace GabesWebTesting.Extraction
{

    public class ExtractArrayFields : ExtractionRule
    {
        public const string ArrayRootElementPlaceholderName = "root";

        public bool Required { get; set; }
        
        public string FullyQualifiedNameAttributeValueUpToArrayName { get; set; }

        public override void Extract(object sender, ExtractionEventArgs e)
        {
            if (!e.Response.IsHtml)
            {
                e.Success = !Required;

                return;
            }
            var tagsForArrayIndexes = GetHtmlTagsFromArrayFields(e.Response, FullyQualifiedNameAttributeValueUpToArrayName);

            if (tagsForArrayIndexes.Any())
            {
                e.Success = true;
                e.WebTest.Context[ContextParameterName] = tagsForArrayIndexes;
            }
            else
            {
                e.Success = !Required;
                e.Message = string.Format("No array tags for array {0}.", FullyQualifiedNameAttributeValueUpToArrayName);
            }
        }

        internal static IEnumerable<IDictionary<string, HtmlTag>> GetHtmlTagsFromArrayFields(WebTestResponse response, string fullyQualifiedNameAttributeValueUpToArrayName)
        {
            if (!response.IsHtml)
            {
                return Enumerable.Empty<IDictionary<string, HtmlTag>>();
            }
            var startsWith = fullyQualifiedNameAttributeValueUpToArrayName + "[";
            var tagsForArrayIndexes = new List<IDictionary<string, HtmlTag>>();
            foreach (var tag in response.HtmlDocument.HtmlTags)
            {
                var name = tag.GetNameAttributeValue();
                var doesStartWith = name.StartsWith(startsWith);
                if (!doesStartWith)
                {
                    continue;
                }
                var indexAndSuffix = name.Substring(startsWith.Length, name.Length - startsWith.Length);
                if (string.IsNullOrWhiteSpace(indexAndSuffix))
                {
                    continue;
                }
                var indexStr = string.Concat(indexAndSuffix.TakeWhile(c => !c.Equals(']')));
                int index;
                if (!int.TryParse(indexStr, out index) || index < 0)
                {
                    continue;
                }
                var suffix = indexAndSuffix.Substring((indexStr + "]").Length,
                    indexAndSuffix.Length - (indexStr + "]").Length).Trim('.');
                var arrayElemName = !string.IsNullOrWhiteSpace(suffix) ? suffix : ArrayRootElementPlaceholderName;
                if (tagsForArrayIndexes.Count == 0 || index >= tagsForArrayIndexes.Count)
                {
                    tagsForArrayIndexes.Add(new Dictionary<string, HtmlTag> { { arrayElemName, tag } });
                }
                else if (tagsForArrayIndexes[index].ContainsKey(arrayElemName)
                    || tagsForArrayIndexes[index].ContainsKey(string.Format("{0}.{1}", tag.Name, arrayElemName))
                    || tagsForArrayIndexes[index].ContainsKey(string.Format("input[type={0}].{1}", tag.GetAttributeValueAsString("type"), arrayElemName)))
                {
                    if (tag.Name.Equals("input") && tag.Attributes.Any(a => a.Name.Equals("type")))
                    {
                        tagsForArrayIndexes[index].Add(
                            string.Format("input[type={0}].{1}", tag.GetAttributeValueAsString("type"), arrayElemName),
                            tag);
                    }
                    else
                    {
                        tagsForArrayIndexes[index].Add(
                            string.Format("{0}.{1}", tag.Name, arrayElemName),
                            tag);
                    }
                }
                else
                {
                    tagsForArrayIndexes[index].Add(arrayElemName, tag);
                }
            }
            return tagsForArrayIndexes;
        }
    }
    
    public static class HtmlTagExtensions
    {
        /// <summary>
        /// Gets the value for name attribute of the specified <see cref="HtmlTag"/>.
        /// </summary>
        /// <param name="htmlTag"></param>
        /// <returns>Defaults to empty <see cref="String"/>.</returns>
        public static string GetNameAttributeValue(this HtmlTag htmlTag)
        {
            if (htmlTag == null)
            {
                return string.Empty;
            }
            return htmlTag.GetAttributeValueAsString("name") ?? string.Empty;
        }
    }
}