Measuring test-coverage tells you almost nothing of value. A disciplined approach leads to high test-coverage. The resulting tests add a lot of value to the development environment.
That correlation isn't something on which you can count, though.
It's like measuring the sharpness of knives in a kitchen. A good cook is going to keep their knives sharp all the time. An amateur cook will probably ignore the a report that their knives are too dull.
The same is true of test-driven development. You're either a professional or you aren't. Either way, test-coverage isn't going to change it.
Most of the time, organizations that are tracking test-coverage end up with something worse than no tests: vast tracts of useless tests that increase cost while providing no real protection.
