public static function validate() {
		$instance = static::get_instance();
		$error = new \WP_Error();
		foreach ( get_class_methods( $instance ) as $method ) {
			$repl = new \ReflectionMethod( get_called_class(), $method );
			// Check if method is public.
			if ( ! $repl->isPublic() ) {
				continue;
			}
			// Check if method start with 'test_'.
			if ( 0 !== strpos( $method, 'test_' ) ) {
				continue;
			}
			$result = call_user_func( [ $instance, $method ] );
			if ( is_wp_error( $result ) ) {
				$error->add( $result->get_error_code(), $result->get_error_message() );
			}
		}
		return $error->get_error_messages()? $error : true;
	}