The assertion has been made that typical applications have between 40%-50% of their code actually run during testing.

I am curious to see what percentage of code you test (actually run during development/unit test/system testing) for:

1) The development of a system from scratch.


2) The development of a new/replacement system but using code parts (including classes, functions, etc.) from existing and well-running systems.


3) Developing revisions to an existing application.


Thanks for your reply.