I've been using Google Apps Script for years. I've been successfully using HtmlService.createHtmlOutputFromFile for months. But a few weeks ago, code that has been working for months stopped working. No HTML is rendered at all.

I created a very small test case.

test.gs

function doIt()
{
  var htmlOutput = HtmlService.createHtmlOutputFromFile('test');
}

test.html

The code is here. https://docs.google.com/spreadsheets/d/1R0EZaHZyR9uUOU6iawc56Tq_lDAmU1aNvWqy9Emluq8/edit?usp=sharing

The problem: No HTML is rendered. Any ideas?

Clarification

This is not being deployed as a web service. It is simply a standalone Google Sheets script. So, I open Google Sheets, then I go into the Apps Script editor, run the function doIt, and I should get HTML rendered on the Google Sheet. And, until a few weeks ago, I did. But now, I get nothing.