I'm designing a ZigBee based product, do I need to get this certified/tested for compliance to the ZigBee standard?

If you wish to use the ZigBee logo then your product must undergo certification. Test programs are available for public profiles which allow interoperability, as also for private profiles (no interoperability). After successful completion of the tests you can use the ZigBee logo on your products.

However, if your product is not required to interoperate with anyone else's products, and you do not want to use the ZigBee logo, then certification is not mandatory. Further information about certification can be found at the ZigBee Alliance website:

http://www.zigbee.org/en/certification/certification_faq.asp