The eID developer smart cards behave for some aspects like the real Belgian eID card, Kids ID or resident cards. They can be used for development and testing purposes. However the final testing of an application needs to be done with real cards.
To find more information on the set of 5 test cards and how to buy them please consult https://www.eazysign.be/en/eazyset-your-set-of-eid-testing-cards
Information about the cards and certificates
The cards work with the official eID middleware: https://eid.belgium.be/
PIN unblock tool: pintool
Frequently asked questions: faq
Developer site: https://github.com/Fedict/eid-mw/wiki/Development
All certificates information can be found here: https://repository.eidpki.belgium.be/#/terms