Unit Testing Mvc6 TagHelpers

I created several custom Mvc6 TagHelpers and I would like to test their outputs other than on the app.

I've been trying to set up a Unit Test but I'm unable to mock the TagHelperContext.

[Fact]
public void TextboxTagHelperTest()
{
    var t = new TextboxTagHelper();
    var m = new Model1();
    var attr = new TagHelperAttributeList();
    attr.Add(new TagHelperAttribute("asp-for", m.MyProperty));
    var thc = new TagHelperContext(attr, new Dictionary<object, object>(), "");
    var o = new TagHelperOutput("united-textbox", attr, null);

    t.Process(thc, o);

    Debug.Write(o);
}

As anyone set up a Unit Test for Mvc6 TagHelpers?