Yes, you can run the work flow and test the output target table.
(From the work flow manager, right click on a work flow, and click "run work flow from start".
Once the work flow is successful, view the data in the target to see of the mappings and transformations are working fine.
Just like any other Unit testing, you'll need to identify the records in your source (and target) and the expected results in the target before you run your work flow.
Eg If I want to test a mapping which has the SCD type2 logic, you can run the work flow twice and update the source columns as needed and after running the work flow, check if the current record has been updated correctly and if the new row for a history version of the record has been updated correctly.