I don't normally run the test cmdlets on most Exchange installations. The installation I'm working on this week just installed the Exchange 2010 Management Pack for SCOM. The default installation for this management pack runs the test cmdlets every 5 minutes.
By default Exchange 2010 does not have users created to use for the testing done by some of the CMDlets. So, you need to run new-testCasConnectivityUser.ps1 from the scripts folder to create them.
This script normally creates users in the "users" container. However, it uses a relative path which fails if there are multiple "users" OUs in your AD structure.
To resolve the issue, either make the "users" container unique or edit the script to use the distinguished path "CN=Users,DC=domain,DC=com"
However, this guy figured it out first: http://www.snowland.se/2010/01/19/problems-with-new-testcasconnectivityuser-ps1/