A good way to test your scripts or application installs in a deployment environment is to use a debug task sequence, Dan over at The Deployment Guys blog posted this http://blogs.technet.com/b/deploymentguys/archive/2011/11/04/zti-mdt-debugger-1-0.aspx which you can download an install.
If you want something a little simpler, I use the below command to start a debug task sequence which allows me to access all of the task sequence variables in order to test my scripts or application installs.
“%deployroot%\tools\%architecture%\serviceui.exe” -process:TSProgressUI.exe c:\windows\system32\cmd.exe
To use with MDT, you can just create a blank task sequence and add a run command line step with the above command, this also applies if you are using SCCM without any MDT integration. If you are using SCCM with MDT integrated and what to able to use any custom variables then you sill also need to add your MDT package a the start of the task sequence and ensure that the customsettings.ini file is processed.
I have attached my MDT task sequence which you can import straight into MDT.