RunbookTester.config

To start the Runbook Designer as another user, click Start > All Programs > Microsoft System Center 2012 > Orchestrator, then hold down the SHIFT key and right click on Runbook Designer. Select Run as different user. Enter the account credentials of the other user, and Runbook Designer launches. You can then go to the runbook you want to test and then click Runbook Tester.
Note: Your alternate user must have rights in the Runbook Designer to see the runbook and must be part of the Orchestrator Users group in order to the runbook to load in the Runbook Tester.
You can verify that this account is being used to open and test the runbook by going to the following directory:

C:\Users\<ACCOUNT_NAME>\AppData\Local\Microsoft System Center 2012\Orchestrator

In there you should see an XML file that represents the runbook being edited, and a file named RunbookTester.config that shows that Runbook tester is being opened in that user context.