title: ASP.NET Core custom tag helper is not working
body: <p>I'm new to ASP.NET core. I follow the guide from MS (<a href="https://docs.microsoft.com/en-us/aspnet/core/mvc/views/tag-helpers/authoring?view=aspnetcore-2.2" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/aspnet/core/mvc/views/tag-helpers/authoring?view=aspnetcore-2.2</a>)</p>
  
  <p>This is my helper:</p>
  
  <pre><code>using Microsoft.AspNetCore.Razor.TagHelpers;
  
  namespace DemoApp.TagHelpers
  {
      class TestTagHelper : TagHelper
      {
          public override void Process(TagHelperContext context, TagHelperOutput output)
          {
              output.TagName="div";
              output.Content.Append("Run...");
          }
      }
  }
  </code></pre>
  
  <p>Added <code>@addTagHelper *, DemoApp</code> to <code>_ViewImports.cshtml</code> and added <code>&lt;test&gt;Test&lt;/test&gt;</code> to my view.</p>
  
  <p>But nothing happen...no tag replacing, no break point trigger...</p>
  
  <p>Any ideas?</p>