This test is for online mode users only. Cache mode users use windows desktop search to search mail
use the command below to test exchange search on the server for a specific user
Test-Exchangesearch -id user@contoso.com
if test returns true, indexing is working fine. if false, then indexing needs to be reset with powershell or manually by restarting MS Exchange search service
OR
test against a mailbox database by typing
Test-ExchangeSearch -MailboxDatabase “databasename” -indexingtimeout 30