checkVariousAuthoredByValues example

    $body_key = 'body[0][value]';
    $edit = [];
    $edit['title[0][value]'] = $this->randomMachineName(8);
    $edit[$body_key] = $this->randomMachineName(16);
    $this->drupalGet('node/add/page');
    $this->submitForm($edit, 'Save');

    // Check that the node was authored by the currently logged in user.     $node = $this->drupalGetNodeByTitle($edit['title[0][value]']);
    $this->assertSame($this->adminUser->id(), $node->getOwnerId(), 'Node authored by admin user.');

    $this->checkVariousAuthoredByValues($node, 'uid[0][target_id]');

    // Check that normal users cannot change the authored by information.     $this->drupalLogin($this->webUser);
    $this->drupalGet('node/' . $node->id() . '/edit');
    $this->assertSession()->fieldNotExists('uid[0][target_id]');

    // Now test with the Autocomplete (Tags) field widget.     /** @var \Drupal\Core\Entity\Display\EntityFormDisplayInterface $form_display */
    $form_display = \Drupal::entityTypeManager()->getStorage('entity_form_display')->load('node.page.default');
    $widget = $form_display->getComponent('uid');
    $widget['type'] = 'entity_reference_autocomplete_tags';