How to verify Avalon-MM slave?

I have written my first Avalon-MM slave component. It shall interface with a Nios II as the master device.

I am a bit lost on how to verify it to make sure that the Nios II shall correctly communicate with it.

I have come across something called BFM, it seems to be a new discipline to use them. I am VHDL-person.

What steps should I take to learn and prepare a testbench to verify this Avalon-MM slave component.