> Writing that test for the single expression setter won't cost you a lot.

Yeah, usually it won't cost anything to the guy who writes the test, but he is actually paid. What it costs to the business/customer/etc and whether the value added is worth of the cost is totally different matter.

I think there is clear incentive for writing unnecessary tests for certain developers - it is non-risky general work, where it is is difficult to fuck up anyway. If you are able to sell test-writing hours, what's the downside?