How to instantiate autowired services in Symfony?

I want to instantiate OrderAbstraction service which requires entity manager in constructor in a test case.

class OrderAbstraction
{
    ...

    /**
     * @var EntityManager
     */
    private $em;

public function __construct(EntityManager $em)
    {
        $this->em = $em;
        ...
    }
}

I've tried to autowire OrderAbstractionTest and give a OrderAbstraction and entity manager as parameter.

class OrderAbstractionTest extends TestCase
{
// tried with constructor and without it
    public function testDays(){
        $order = new OrderAbstraction();
        $order->dateFrom(new \DateTime('2019-08-20 14:00'));
        $order->dateTo(new \DateTime('2019-08-28 14:00'));

        $days = $order->days();
        $this->assertEquals(8, $days);
    }
}

my service.yaml, autowire set to true

    App\Service\OrderAbstraction\:
        resource: '../src/Service/OrderAbstraction.php'
        arguments: 
            $em: '@Doctrine\ORM\EntityManager'

    App\Test\OrderAbstraction\:
        resource: '../tests/OrderAbstractionTest.php'
        arguments: 
            $em : '@Doctrine\ORM\EntityManager'

I keep getting something like this PHP Fatal error: Uncaught ArgumentCountError: Too few arguments to function App\Test\OrderAbstractionTest::__construct(), 0 passed in /var/www/html/autocom/bin/.phpunit/phpunit-6.5/src/Framework/TestSuite.php on line 476 and exactly 1 expected in /var/www/html/autocom/tests/OrderAbstractionTest.php:13

Would be great to know how to instantiate OrderAbstraction services, test. Because most of the I do something like this in controllers:

$order = new OrderAbstraction($this->em);