I developed a software using some OSM data. It is normally required to make the extracted OSM data available to customer, who
can spread it for free.
Thats clear - also that notification (webpage/software) shows where data comes from.
But what if I offer the customer a free of charge test of the service/software. Is it required to offer the data to the tester also for free&completely after such a free-of-charge-test?!
I am afraid it is. Or not?
In my opinion a free of charge-test is a test of a service not a service itself…
You must release your OSM derived data under the same license you get access to those data, so any single customer has the right to put the data you sold available for download. I shouldn’t say “spread it for free”, but an exercise of his rights, the same rights that every OSM contributor gives to you, and you could use that rights to distribute your derivative work.
You can provide the service or the software under other terms, free (during a a test or lifetime)or for a fee, but the derived data remains under ODBL.