New Twiddle

controllers.application.js

import Controller from '@ember/controller';
import { computed } from '@ember/object';

const values = [
	0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100
];

export default Controller.extend({
  sliderIndex: 1,

  values: computed('sliderIndex', function() {
    return values.map((v, index) => {
      const value = v;
      const selected = parseInt(this.get('sliderIndex'), 10) === index;
      
      if (selected)
        console.error(value);

      return { value, selected };
    });
	}).readOnly(),
});

modifiers.prop\.js

import { setModifierManager, capabilities } from '@ember/modifier';

function setProps(element, properties) {
  for (let key in properties) {
    element[key] = properties[key];
  }
}

export default setModifierManager(
  () => ({
    capabilities: capabilities('3.13', { disableAutoTracking: true }),

    createModifier() {
      return {
        element: null
      };
    },

    installModifier(state, element, args) {
      state.element = element;
      
			setProps(element, args.named);
    },

    updateModifier(state, args) {
      setProps(state.element, args.named);
    },
    destroyModifier() {},
  }),
  
  class PropModifier {}
);

templates.application.hbs

<h2>{{sliderIndex}}</h2>
{{input type="range" min="0" max="10" value=this.sliderIndex}}

<select value="target.value">
  {{#each this.values as |value index|}}
    <option value="{{index}}"
      {{prop selected=value.selected}}>
    {{value.value}} {{value.selected}}
    </option>
  {{/each}}
</select>

tests.helpers.destroy-app.js

import Ember from 'ember';

export default function destroyApp(application) {
  Ember.run(application, 'destroy');
}

tests.helpers.resolver.js

import Resolver from '../../resolver';
import config from '../../config/environment';

const resolver = Resolver.create();

resolver.namespace = {
  modulePrefix: config.modulePrefix,
  podModulePrefix: config.podModulePrefix
};

export default resolver;

tests.helpers.start-app.js

import Ember from 'ember';
import Application from '../../app';
import config from '../../config/environment';

const { run } = Ember;
const assign = Ember.assign || Ember.merge;

export default function startApp(attrs) {
  let application;

  let attributes = assign({rootElement: "#test-root"}, config.APP);
  attributes = assign(attributes, attrs); // use defaults, but you can override;

  run(() => {
    application = Application.create(attributes);
    application.setupForTesting();
    application.injectTestHelpers();
  });

  return application;
}

tests.test-helper.js

import resolver from './helpers/resolver';
import {
  setResolver
} from 'ember-qunit';

setResolver(resolver);

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.17.0",
    "ember-template-compiler": "3.17.0",
    "ember-testing": "3.17.0"
  }
}