I don't believe it excludes test user data by default, so you should be able to report on it. There is actually a data item in the data warehouse found here: Expense>Lists>Employee Information>Additional Details. In here you will see an item named: Is Test User. I would add this item to the report I was building, then filter on this item to only show "Y" for Yes. This will show only Test Users. Remember that most likely you won't see any data results if you add any data items that indicate the report has been Processor approved. For example, you won't want to add Sent for Payment Date or Paid Date since Test User reports don't show up in the Processor queue.
I hope this helps.