How can I use Behat to set the value of a CKEditor 5 field?

I'm trying to use Behat to set the value of a CKEditor 5 field. I am using CKEditor 5 with Drupal 9.

For CKEditor 4, I used a gist by johnennewdeeson:

  /**
   * @Then I fill in wysiwyg on field :locator with :value
   */
  public function iFillInWysiwygOnFieldWith($locator, $value) {
    $el = $this->getSession()->getPage()->findField($locator);

    if (empty($el)) {
      throw new ExpectationException('Could not find WYSIWYG with locator: ' . $locator, $this->getSession());
    }

    $fieldId = $el->getAttribute('id');

    if (empty($fieldId)) {
      throw new Exception('Could not find an id for field with locator: ' . $locator);
    }

    $this->getSession()
      ->executeScript("CKEDITOR.instances[\"$fieldId\"].setData(\"$value\");");
  }

This works great with CKEditor 4, but when I try to do the same thing with CKEditor 5, I get the following error:

CKEDITOR is not defined

How can I set the value of CKEditor 5 in Behat/Mink?

As described in How to get the editor instance object from the DOM element?, you can search for ck-editor__editable and use that to locate the specific editor instance that you need to manipulate.

So the code looks like this:

    $this->getSession()
      ->executeScript(
        "
        const domEditableElement = document.querySelector(\"$MY_SELECTOR\");
        if (domEditableElement.ckeditorInstance) {
          const editorInstance = domEditableElement.ckeditorInstance;
          if (editorInstance) {
            editorInstance.setData(\"$value\");
          } else {
            throw new Exception('Could not get the editor instance!');
          }
        } else {
          throw new Exception('Could not find the element!');
        }
        ");