Multiple PostgreSQL instances on one machine

I am trying to consolidate some machines in my server room particularly in
the testing environment and I was hoping someone could point me in the
right direction.

I currently have three machines running PostgreSQL for testing purposes.
Each week a backup is made of the production database and this is deployed
onto these three machines. None of these machines is any where near
capacity. I would like to host all three instances on one machine.

I know that "initdb" can be used to create additional installations, but
the part I am unsure about is the tablespace. The production database has
a tablespace defined that resides on its SSD. When I use the production
backup, I have to create a mount point on the test machine with the same
name as the one on the production database. I am not certain how I would
handle this situation if I am serving three separate instances of that
database from one computer.