I am giving this answer by considering product not base on project oriented.

If suppose, product has developed in Oracle 8i environment, and new customer
wants the same product in Oracle10g.

As a Database tester, we should test the product in Oracle 10g environment. For
that you need to install Oracle 10g, Administrator will install 10g, Your role
is to create one new schema in 10g and run the functions and procedures on that,
export and import all these things comes under your work.

If you get any good answers, you can forward the answer to my mail id
mentioned below

Regards

Suresh.Vemparala