Jetpack_Heartbeat::init PHP Method

    public static function init()
    {
        if (!self::$instance) {
            self::$instance = new Jetpack_Heartbeat();
        }
        return self::$instance;
    }

 /**
  * @covers Jetpack_Heartbeat::cron_exec
  * @since 3.9.0
  */
 public function test_cron_exec()
 {
     $this->heartbeat_action = false;
     add_action('jetpack_heartbeat', array($this, 'jetpack_heartbeat'));
     Jetpack_Heartbeat::init()->cron_exec();
     $this->assertTrue($this->heartbeat_action);
 }