I think that the title says a lot in this case.
I have a Team Foundation Server and I have a Test Controller registered to it.
I also have Test Agents – they hang out in the lab (not in the production domain with the TFS Server or the Test Controller) so I need to have authenticated communication between the Agents and the Controller.
The most likely scenario is; the Test Controller is in the same domain as the TFS application server (assuming the TFS application server is in your production domain) and the Test Agents are not, nor is there a domain trust.
The Agents could be / should be in most any domain and most likely will execute their tests within an isolated test domain.
Installation and configuration of the Test Agent always requires local administrator rights, it is registration of the Test Agent with a remote Test Controller that can involve unique combinations.
If the Test Agent machine and the Test Controller machine are not joined to the same Active Directory domain or they are not joined to fully trusted domains (or the Agent machine is not domain joined) then:
1) Create local computer account on the Test Controller and each Test Agent machine to provide authentication.
2) This local account should have the same username and password across the Test Controller and Test Agent machines.
3) The “password never expires” check box should be checked.
4) When configuring the Test Agent username do not include the name of the local machine (machinename\username) use only the username (username).
Installation using the common local user account:
a. If this local user account is used to install the Test Agent software then the user account should be assigned to the local administrator security group of the Test Agent machine.
i. If this local user account is used to configure the Test Agent and register it with the Test Controller the local user account should be assigned to the local administrator security group on both the Test Agent and Test Controller machines.
Installation using an administrator account (not the common local user account):
1) The local administrator account can be used to install the Test Agent on the agent machine(s) as long as the local administrator user account password is the same on the Test Controller and Test Agent machines.