u should install same version of informix at test site and u should not initialize database.
transefer the backed up file to test site set TAPEDEV parameter in configuration file to where u copy the backed up file.
then give the command ontape -r it wil prompt u for wich level ,u have to specify the level which u backed up (zero) then it wil prompt u logical resote, if u backed up logs at primary site that file is to be trasfered to test site and set parameter LTAPEDEV parameter in onconfig file. then u say yes logs also restored
Just a little more to what mariadasun gave you; your test environment has to have the same dbspaces (name and size) and the same number of logical logs as the environment from where you took the backup.