What exactly is a "roadworthy test"?
Exactly what it says on the box. A check, typically yearly of the car for roadworthyness. Each country implements it differently. Netherlands (Algemene Periodieke Keuring), Germany (Kfz-Zulassungen und Hauptuntersuchung), Belgium (Autokeuring), Luxembourg and France (Contrôle Technique), Spain (Inspección Técnica de Vehículos), etc.
Quite a few of them check e-call functionality as a mandatory check along with a whole host of other tests, brake checks and gap measurements, tire tread tests, steering checks, light bulbs, etc. In most cases people combine their roadworthy test with a quick maintenance visit to save them going to the workshop at a different time.
It's not a European thing alone. It's also required in Australia, New Zealand, even China (for vehicles over 10 years old),