In a large codebase it's not a given indeed. That's why you want integration tests to get there.

This is an old one but still a funny way to approach the question of test coverage. Unsurprisingly, the context matters.

Or why meeting targets is not what you want. It's still a good guide though.

This is indeed a good way to guide your debugging. Using coverage information can sometimes reduce the search space.

Interesting bug in SQLite. In particular look for the conclusion regarding tests and coverage. It's something I often have to remind people of.