if (x > 0) {
/* code */
} else {
/* more code */
}
Branch coverage just means that all the lines above are executed in some test. That's fundamentally different from dealing with all the different values that `x` could take on at run time.
Given your example no software can ever handle this equation given infinite numbers, as all CPUs have a maximum number they can compare.
Just like you cannot prove that a bridge will be able to handle a given load. Engineering fundamentally can only make assurances within expectations. Your tests define these expectations, and by covering 100% branching coverage you've exhaustively explored all valid states your software can have.
Do note I'm talking about actual 100% branching coverage here, not just 100% coverage of your own code, ignoring libraries and runtimes you've imported. That's way harder then you seem to think and the reason why sqlite (the linked page) has so much more testing code then application code
