I discovered for my self that the best time to add tests to a project is when you cant overlook everything anymore and you ran into problems when you add one fe

I discovered for my self that the best time to add tests to a project is when you cant overlook everything anymore and you ran into problems when you add one feature on one side and on the other a whole house breaks down. There is no need to write tests for fast moving objects and for this kind of work TDD is a waste of time in my opinion. But for core infrastructure this makes sense. But driving blind all the time is not a good idea on the long run.