unloadAll test

components.my-component\.js

import Component from '@glimmer/component';
import { tracked } from '@glimmer/tracking';

export default class extends Component {
  @tracked fooModel = null;
}

controllers.application\.js

import Controller from '@ember/controller';
import { action } from '@ember/object';
import { inject as service } from '@ember/service';
import { tracked } from '@glimmer/tracking';

export default class ApplicationController extends Controller {
  @service store
  
  appName = 'Ember Twiddle';

  @tracked fooModel = null;

  @action
	setFooModel() {
    const fooModel = this.store.createRecord('foo', {
      id: 'foo',
      name: 'foo1',
      bars: [
        this.store.createRecord('bar', {
          id: 'bar',
          name: 'bar1'
        })
      ]
    }); 
    this.fooModel = fooModel;
  }
  
  @action
	unloadAllRecords() {
    this.store.unloadAll();
    this.fooModel = null;
  }
}

models.bar\.js

import Model from 'ember-data/model';
import attr from 'ember-data/attr';
/*
import attr from 'ember-data/attr';
import { belongsTo, hasMany } from 'ember-data/relationships';
*/

export default class extends Model {
  @attr('string') name
}

models.foo\.js

import Model from 'ember-data/model';
import attr from 'ember-data/attr';
import { hasMany } from 'ember-data/relationships';
/*
import attr from 'ember-data/attr';
import { belongsTo, hasMany } from 'ember-data/relationships';
*/

export default class extends Model {
  @hasMany('bar') bars
  @attr('string') name
}

templates.application\.hbs

<h1>Welcome to {{this.appName}}</h1>
<br>
<br>
{{#if fooModel}}
  <button type="button" {{on 'click' (fn this.unloadAllRecords)}}>Unload Records</button>
{{else}}
  <button type="button" {{on 'click' (fn this.setFooModel)}}>Set Model</button>
{{/if}}
<br><br>

<MyComponent @fooModel={{fooModel}} />

templates.components.my-component\.hbs

{{#if @fooModel}}
fooModel id: {{@fooModel.id}}
<br>
fooModel name: {{@fooModel.name}}
<br>
fooModel bars:
{{#each @fooModel.bars as |bar|}}
<br>{{bar.name}}<br>
{{/each}}
{{/if}}

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0",
    "ember-data": "3.18.0"
  }
}