we need to write our own activities to delete the workobjects (RDB methods)

delete from pc_data_uniqueid@
update pc_data_uniqueid set pylastreservedid=0@
delete from pc_work@
delete from pc_assign_worklist@
delete from pc_assign_workbasket@
delete from pc_history_work@
delete from pc_data_workattach@
delete from pc_index_workparty@
delete from pc_link_attachment@
delete from pc_link_folder@
commit@

There is no option in the dashboard to delete cases. 

The standard Pega solution for cases is to Resolve-Withdraw cases that are "deleted" for production systems.

Is this a development question on how to delete test cases you created along the way?

 You can run an activity that loops through a list of cases (obtained from a report definition) and calls pxForceCaseClose to Complete all of the work. You will pass the desired resolved status (for example, Resolved-Complete) as a parameter.  Set the Commit parameter to true. Then you can use the wizard to delete the cases.

We have chosen to use the archive utility on Exhange to purge cases more easily. We simply do not configure the archive.