I know Mika Hakkinen left a race seat for a test role at McLaren after (I think) two seasons. And, like Alonso, it didn’t do him much harm, did it?!
Presumably you mention this because of Nico Hulkenberg’s situation. I think he should consider moving to Mercedes to be their 3rd driver. OK, so he’ll get next to no test time, but I think it’s safe to assumer Michael Schumacher is closer to the end of his career than the start, and therefore a vacancy that looks like it was made for the Hulk will be coming up in the near future