A couple of customers have reported that their unit tests were not running when Team Builds based on TfvcTemplate.12.xaml ran (may happen with other templates too). The build definition looked just fine, but the tests just did not execute. We came to find that the team build definition\template doesn't appear to respect test parameters entered directly into the Property Grid. For example, in the picture below the customers had typed the values directly in.
Workaround is to use the ellipsis button wherever possible (for example, to browse to the settings file in version control) rather than hand-typing your values.