Unit testing code coverage - do you have 100% coverage?

Question

Do your unit tests constitute 100% code coverage? Yes or no, and why or why not.

Answer 1

To all the 90% coverage tester:

The problem with doing so is that the 10% hard to test code is also the not-trivial code that contains 90% of the bug! This is the conclusion I got empirically after many years of TDD.

And after all this is pretty straightforward conclusion. This 10% hard to test code, is hard to test because it reflect tricky business problem or tricky design flaw or both. These exact reasons that often leads to buggy code.

But also:

• 100% covered code that decreases with time to less than 100% covered often pinpoints a bug or at least a flaw.
• 100% covered code used in conjunction with contracts, is the ultimate weapon to lead to live close to bug-free code. Code Contracts and Automated Testing are pretty much the same thing
• When a bug is discovered in 100% covered code, it is easier to fix. Since the code responsible for the bug is already covered by tests, it shouldn't be hard to write new tests to cover the bug fix.