MockHTMLElement is missing animate method

[JonasMa]

Stencil version:

 @stencil/core@2.3.0

I'm submitting a:
[x] bug report
[ ] feature request
[ ] support request => Please do not submit support requests here, use one of these channels: https://stencil-worldwide.herokuapp.com/ or https://forum.ionicframework.com/

Current behavior:
I am writing jest tests for my web-components. I,m animating HTMLElelements with the animate method. It works fine when I create the component in the browser in normal way, But it breaks if I create the component in my unit tests using newSpecPage interface. The reason for breaking is that jest in stencil replace normal DOM with MockDOM and the mockHTMLElement on which I am using animate is missing the method animate

Expected behavior:
MockHtmlElement should have all the methods of an HTMLElement

Steps to reproduce:
1- Create a simple component, use animate on any Element
2- Run unit tests over the component

Related code:

my-component.spec.ts

 it('should work',()=>{
   const myComponent = await newSpecPage({
        components: [MyComponent],
        html: `<my-component></my-component>`
   }); // throws ERROR
   expect(myComponent.root.querySelector('#test')).notToBeNull(); // fails
 });

my-component.tsx

@Component({
    tag: 'my-component'
})
export class MyComponent {
@Element() rootElem:HTMLElement;

    componentDidLoad() {
      // throws TypeError: this.rootElem.animate is not a function
      // this.rootElem is of type MockHTML element when run from test else HTMLELement
      this.rootElem.animate([{ transform: 'rotate(90deg)' }]);
    }


    render() {
        return (
            <div id="container">
            </div>
        );
    }
}

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