What exactly is it wasting? Is your screen going to run out of ink? Even in the physical contruction world, people often build as much or more scaffolding as the thing they're actually building, and that takes time and effort to put up and take down, but it's worthwhile.
Sure, maybe you can do everything you would do via TDD in your head instead. But it's likely to be slower and more error-prone. You've got a computer there, you might as well use it; "thinking aloud" by writing out your possible API designs and playing with them in code tends to be quicker and more effective.
Time. Writing and maintaining low level unit tests takes time. That time is an investment. That investment does not pay off.
Doing test driven development with high level integration tests also takes time. That investment pays dividends though. Those tests provide safety.
>Sure, maybe you can do everything you would do via TDD in your head instead. But it's likely to be slower and more error-prone.
It's actually much quicker and safer if you can change designs under the hood and you dont have to change any of the tests because they validate all the behavior.
Quicker and safer = you can do more iterations on the design in the available time = a better design in the end.
The refactoring step of red, green, refactor is where the design magic happens. If the refactoring turns tests red again that inhibits refactoring.
Sure, maybe you can do everything you would do via TDD in your head instead. But it's likely to be slower and more error-prone. You've got a computer there, you might as well use it; "thinking aloud" by writing out your possible API designs and playing with them in code tends to be quicker and more effective.