TFS2010 Build does not run unit tests

I have a build definition in TFS2010, I queue the build manually and set Disable Tests flag to False. However, my unit tests are still not getting run. I reviewed the xaml file and it appears fine. The configuration used for the build is "Release". Is there something else that needs to be done? Unit test related snippet:

if Condition="[Not DisableTests]" DisplayName="If Not DisableTests"

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Add some of the build file. Most likely you are either a) missing the custom action to run the tests or b) it is improperly configured.

Check the build definition properity "DisableTests" should be set to false.