Example of the triggerKeyEvent being actively blocked by the browser.

backspace-triggerkeyevent-test.js

import { module, test } from "qunit";
import { setupRenderingTest } from "ember-qunit";
import { render, typeIn, triggerKeyEvent } from "@ember/test-helpers";
import hbs from "htmlbars-inline-precompile";

module(
  "Integration | Component | data-properties-panel/custom-property-form",
  function(hooks) {
    setupRenderingTest(hooks);

    hooks.beforeEach(async () => {
      await render(hbs`<input data-test-input type="text"/>`);
    });

    test("it should have backspaced input font", async function(assert) {
      await typeIn("[data-test-input]", "hello world");
      assert.dom("[data-test-input]").hasValue("hello world");
      await triggerKeyEvent("[data-test-input]", "keydown", "Backspace");
      assert.dom("[data-test-input]").hasValue("hello worl");
    });

    module("work around", hooks => {
      const backspaceHandler = e => {
        if (e.key === "Backspace") {
          e.srcElement.value = e.srcElement.value.slice(0, -1);
        }
      };
      hooks.beforeEach(function() {
        document
          .querySelector("[data-test-input]")
          .addEventListener("keydown", backspaceHandler);
      });

      hooks.afterEach(function() {
        document
          .querySelector("[data-test-input]")
          .removeEventListener("keydown", backspaceHandler);
      });

      test("it should have backspaced input font", async function(assert) {
        await typeIn("[data-test-input]", "hello world");
        assert.dom("[data-test-input]").hasValue("hello world");
        await triggerKeyEvent("[data-test-input]", "keydown", "Backspace");
        assert.dom("[data-test-input]").hasValue("hello worl");
      });
    });
  }
);