It may or may not happen that I end up working with them on one of their big global clients, but I unfortunately didn't confirm with them before doing the "test" work (about a day's worth) that I would of course be invoicing for this test assignment, regardless of their decision to bring me in or not to help with their client. The test assignment was of course also real-life content for the client.
I've done these kinds of "test" assignments for creative and ad agencies in the past who had approached me and in both cases, those agencies both said at some point during the initial conversation things to the effect of, "We'll of course pay you" or "Just send us an invoice ..."
Unfortunately with this current ad agency, the invoice or topic of payment never came up. It just naturally didn't and I didn't even think of it for the hour we were chatting to be honest. But I've now done the work and I still plan on invoicing them for my day rate, regardless of if they use me or not.
My question though for people here, is it typical for someone in my case to invoice in such circumstances? To me it is and obviously to the previous two agencies I've done these kinds of test assignments for, it was normal and expected for me to do so.