FUnit::setup() and bootstrap files

This is more a point of clarification. In the docs you say that FUnit::setup() "Register['s] a function to run at the start of each test."

Does that mean that it's executed before EVERY single closure (having been set by FUnit::test())? Or is it only run at the beginning of every file of tests?

I ask because I was trying to set up a bootstrap file to setup a few fixtures (specifically a DB connection) that were shared between a few tests (spread across a few files) but each fixture kept coming out null until I moved them from a global bootstrap into each test file. This is probably a 'dark corner' of bin/fu not yet explored?