I think you can go one step further. Never forget you're serving your customers, and your software has other raison d'etre. You only write software to provide value to them, so think of testing the same way.
Each test has the opportunity cost of writing some part of a new feature for your customers. But so does every minute spent of fixing bugs that would have been caught with more testing, at a fraction of the cost.
Each test has the opportunity cost of writing some part of a new feature for your customers. But so does every minute spent of fixing bugs that would have been caught with more testing, at a fraction of the cost.