how to test application impersonation in exchange 2010?

It depends what you mean by test (one line questions aren't a good idea use the forum guide https://social.technet.microsoft.com/Forums/office/en-US/77c07b69-eea6-43ab-9225-4b384cecfc9d/exchange-development-forum-guide-read-before-posting?forum=exchangesvrdevelopment to help you ask a better question) ?

You can test if impersonation works using the EWSEditor https://ewseditor.codeplex.com/ also https://testconnectivity.microsoft.com/ has the ability to test impersonation using the Service Account Access (Developers) option

Cheers
Glen