I'm trying to understand what you are trying to do ? However

You can restore a single tablespace from a full db backup image but not
redirect in the database that the inage came from so that you could "see"
two tablespaces (one existing and the same redirected). If you redirect in
the same db the table and data of the existing tablespace will not be
accessible as the tblspce has been restored elsewhere.
The best you could do is to restore  fom the image in your test database.
Extract (export, db2move) the data out of that and then move those tables
into a new tablespace on the target db.

HTH,  Pierre.