[ay]

test coverage is calculated as % of the locations seen by profiler during the test runs, right ?

This metric completely ignores the fact that every independent conditional doubles the space of the behaviors of the program.

Assuming we have three conditions and three sequential groups of basic blocks chosen corresponding to true (X) and false (~X) values of these conditions, testing A+B+C and ~A+~B+~C code paths gives 100% code coverage but it covers at the very best only 25% of the code behaviors.

[dalke]

There are many types of test coverage measurement. I believe path coverage ("Has every possible route through a given part of the code been executed?") is your latter example. Quoting https://en.wikipedia.org/wiki/Code_coverage which also says:

> Full path coverage, of the type described above, is usually impractical or impossible. ... a general-purpose algorithm for identifying infeasible paths has been proven to be impossible (such an algorithm could be used to solve the halting problem).[14] Basis path testing is for instance a method of achieving complete branch coverage without achieving complete path coverage."