class NodeEntityViewModeAlterTest

class NodeEntityViewModeAlterTest extends NodeTestBase {
  use EntityViewTrait;
  
  /**
   * Enable dummy module that implements hook_ENTITY_TYPE_view() for nodes.
   */
  protected static $modules = [
    'node_test',
  ];
  
  /**
   * {@inheritdoc}
   */
  protected $defaultTheme = 'stark';
  
  /**
   * Create a "Basic page" node and verify its consistency in the database.
   */
  public function testNodeViewModeChange() {
    $web_user = $this->drupalCreateUser([
      'create page content',
      'edit own page content',
    ]);
    $this->drupalLogin($web_user);
    // Create a node.
    $edit = [];
    $edit['title[0][value]'] = $this->randomMachineName(8);
    $edit['body[0][value]'] = 'Data that should appear only in the body for the node.';
    $edit['body[0][summary]'] = 'Extra data that should appear only in the teaser for the node.';
    $this->drupalGet('node/add/page');
    $this->submitForm($edit, 'Save');
    $node = $this->drupalGetNodeByTitle($edit['title[0][value]']);
    // Set the flag to alter the view mode and view the node.
    \Drupal::state()->set('node_test_change_view_mode', 'teaser');
    Cache::invalidateTags([
      'rendered',
    ]);
    $this->drupalGet('node/' . $node->id());
    // Check that teaser mode is viewed.
    $this->assertSession()
      ->pageTextContains('Extra data that should appear only in the teaser for the node.');
    // Make sure body text is not present.
    $this->assertSession()
      ->pageTextNotContains('Data that should appear only in the body for the node.');
    // Test that the correct build mode has been set.
    $build = $this->buildEntityView($node);
    $this->assertEquals('teaser', $build['#view_mode'], 'The view mode has correctly been set to teaser.');
  }

}