Debate in my town: New diesel emissions testing rule splitting opinions

The county just announced required emissions testing for all diesel vehicles over 5 tons. Some mechanics at my local shop support it, saying it will cut down on smoke from older engines. Others argue it makes owners pay for fixes on trucks that still work fine. For instance, a nearby farm has two tractors that might fail the test, costing a lot to fix. But the city buses get a pass, which seems unfair. What do you all think about this rule?