I am not sure if this is yet possible or not as this requires Microsoft federation gateway , is there a way to simulate Federated Sharing in exchange 2010 lab prior to implementation in production ? please suggest ? &nb

Hi,

We can use Exchange LoadGen to simulate the delivery of multiple MAPI client messaging requests to an Exchange server, please refer to:
https://social.technet.microsoft.com/Forums/exchange/en-US/abb345a8-cfeb-46d6-b8e2-3354c083be60/tool-to-simulate-email-traffic
Unfortunately, we have not a tool to simulate federated sharing before implementation. If you want to deploy Federated Service, please refer to AD FS Deployment Guide:
https://technet.microsoft.com/en-us/library/cc771833(v=ws.10).aspx

By the way, we can use Test-FederationTrust to verify that the federation trust is properly configured and functioning as expected, for your reference:
https://technet.microsoft.com/en-us/library/dd979787(v=exchg.150).aspx

Best Regards,
Allen Wang