extensionConfig example

  protected function setUp(): void {
    parent::setUp();
    $this->installConfig(['system']);
  }

  /** * Verifies that no themes are installed by default. */
  public function testEmpty() {
    $this->assertEmpty($this->extensionConfig()->get('theme'));

    $this->assertEmpty(array_keys($this->themeHandler()->listInfo()));
    $this->assertEmpty(array_keys(\Drupal::service('theme_handler')->listInfo()));

    // Rebuilding available themes should always yield results though.     $this->assertNotEmpty($this->themeHandler()->rebuildThemeData()['stark'], 'ThemeHandler::rebuildThemeData() yields all available themes.');

    // theme_get_setting() should return global default theme settings.     $this->assertTrue(theme_get_setting('features.favicon'));
  }