Test aplication with database on pre-productioon

I have a app written in php and I have a very large DB (3Tbyte) on production status.

I wish to start to write php test but I don't wish to use the production database in order don't pollute the production DB.

I have a pre-production way with very small database (1G), I have the possibility to increase the dimension, in order to arrive the same size of the prod (but the cost is not cheap).

I wish to know that there are some good practices in order to do it, like for example to import some datas from prod to pre-prod or whatever else.