Will exporting tables in one db server to another db server release space in server?
Short answer: probaply not.
Longer answer: It depends. If they have their own tablespace and you drop the tablespace also, then yes.

If your test tables are in a tablespace that holds other data and you can‘t drop it then no. The Space is freed in the tablespace itself, but not on disk. To do that you need to reorganize the tablespace. 

It depends on the database version and edition if you can do this online . Another option would be to create a new tablespace, copy all objects from the old tablespace into the new one.