Custom Widget Configuration Property

I changed my code to the below and still just get a plain text box...the Render method never fires.

        public void Render(TextWriter writer, IPropertyTemplateOptions options)
        {
            string defaultOption = "<option value=\"test\" >Search</option>";
            if (options.Value != null)
            {
                defaultOption = "<option value=\"placeholder\" >"+options.Value.ToString() + " </option>";
            }

            string script = "hello world";

            writer.Write(script);
        }

This works for me to display Hello World:

using System.Collections.Generic;
using System.IO;
using Telligent.Evolution.Extensibility.Configuration.Version1;

namespace Samples
{
    public class TestPropertyTemplate : IPropertyTemplate
	{
		#region IPlugin

		public string Name => "Test Template";

		public virtual string Description => $"template test";

		public virtual void Initialize()
		{
		}

		#endregion

		#region IPropertyTemplate

		public string[] DataTypes => new string[] { "Custom" };

		public string TemplateName => "testTemplate";

		public bool SupportsReadOnly => true;

		public virtual PropertyTemplateOption[] Options
		{
			get
			{
				var options = new List<PropertyTemplateOption>();
				return options.ToArray();
			}
		}

		public void Render(TextWriter writer, IPropertyTemplateOptions options)
		{
			string script = "hello world";

			writer.Write(script);
		}
		#endregion
	}
}

Here is the configuration declaration:

	<property id="test" defaultValue="" dataType="Custom" template="testTemplate" />

Since you're in the code already, could you try changing the case of the supported data type to "String" from "string"?