Unit testing typescript web components

Solution for Unit testing typescript web components
is Given Below:

Unit testing typescript web components with karma-typescript and using fixture from @open-wc/testing-helpers causes the following error to happen: ” Uncaught TypeError: Failed to construct ‘HTMLElement’: Please use the ‘new’ operator, this DOM object constructor cannot be called as a function.”

export class ButtonComponent extends HTMLElement {....}

let elem: Element =  await fixture("<button-component></button-component>");

expect(elem).not.toBeUndefined();

Spent so much time resolving error after error and now this one. Not sure what else is needed to make this work.