Im am looking for a tool/methodology free or otherwise for testing performance at the development stage.

From what I understand developers may test for functionality at a Unit level (Junit etc.). It may require many of these "units" of code to be able to test ..something.. for performance.

Eg. A button on a Web Page that writes a particular form to a database may have many units of Code.

How could one test at this level?

I would be grateful to anyone who may point me in the direction of some information.

Yes, Im a fully fledged beginner!

Thank you