fix: treat shadow DOM elements as in the document (#298)

src/__tests__/to-be-in-the-document.js

@@ -2,19 +2,37 @@ import {HtmlElementTypeError} from '../utils'
 import document from './helpers/document'
 
 test('.toBeInTheDocument', () => {
+  const window = document.defaultView
+
+  window.customElements.define(
+    'custom-element',
+    class extends window.HTMLElement {
+      constructor() {
+        super()
+        this.attachShadow({mode: 'open'}).innerHTML =
+          '<div data-testid="custom-element-child"></div>'
+      }
+    },
+  )
+
   document.body.innerHTML = `
     <span data-testid="html-element"><span>Html Element</span></span>
-    <svg data-testid="svg-element"></svg>`
+    <svg data-testid="svg-element"></svg>
+    <custom-element data-testid="custom-element"></custom-element>`
 
   const htmlElement = document.querySelector('[data-testid="html-element"]')
   const svgElement = document.querySelector('[data-testid="svg-element"]')
+  const customElementChild = document
+    .querySelector('[data-testid="custom-element"]')
+    .shadowRoot.querySelector('[data-testid="custom-element-child"]')
   const detachedElement = document.createElement('div')
   const fakeElement = {thisIsNot: 'an html element'}
   const undefinedElement = undefined
   const nullElement = null
 
   expect(htmlElement).toBeInTheDocument()
   expect(svgElement).toBeInTheDocument()
+  expect(customElementChild).toBeInTheDocument()
   expect(detachedElement).not.toBeInTheDocument()
   expect(nullElement).not.toBeInTheDocument()
 

src/to-be-in-the-document.js

@@ -6,7 +6,9 @@ export function toBeInTheDocument(element) {
   }
 
   const pass =
-    element === null ? false : element.ownerDocument.contains(element)
+    element === null
+      ? false
+      : element.ownerDocument === element.getRootNode({composed: true})
 
   const errorFound = () => {
     return `expected document not to contain element, found ${this.utils.stringify(