How to access shadowDom when testing Lit element with open-wc - testing

Question

Lit docs refer to Web Test Runner as testing. It navigates to this example page.
I tried testing MyElement, which has only one <p>.
import { LitElement, html } from "lit";
import { customElement } from "lit/decorators.js";
#customElement("my-element")
export class MyElement extends LitElement {
render() {
return html`<p>Hello, World.</p>`;
}
}
declare global {
interface HTMLElementTagNameMap {
"my-element": MyElement;
}
}
When testing by open-wc, the element's shadowDom did not have <p> in descendant.
import { expect, fixture, html } from "#open-wc/testing";
import { MyElement } from "../src/MyElement";
it("get shadowDom", async () => {
const el: MyElement = await fixture(html`<my-element></my-element>`);
expect(el).shadowDom.to.be.not.null; // passed
expect(el).shadowDom.to.have.descendant("p"); // failed
});
Does it need more setup to test Lit elements with open-wc?
web-test-runner.config.js is:
import { esbuildPlugin } from '#web/dev-server-esbuild';
export default {
files: ['test/*.test.ts'],
plugins: [esbuildPlugin({ ts: true })],
};

Answer 1

Try shadowRoot instead of shadowDom:
it("get shadowDom", async () => {
const el = await fixture(
html` <my-element></my-element>`
);
const descendant = el.shadowRoot!.querySelector("p")!;
expect(descendant).to.be.not.null;
});

Answer 2

I had similar issue. In my case shadowRoot was "null". To have shadowRoot content I had to import my web component like that:
import './myWebcomponent';