I only have one piece of code for which I can say true 100% coverage exists: a library that works with HTML/CSS color values, and which ships a test that generates all 16,777,216 hexadecimal and integer rgb() color values, and runs some functions with each value.

However, I don't run that as part of the normal test suite. It only gets run when I'm prepping a new release, as a final verification step; the normal runs-every-commit test suite just exercises with a selection of values likely to expose obvious problems.