Wrapping the code with #if 0 does the trick but then you still need to edit the code to enable/disable it. That’s not much better than just using the comment block.
Note that you can also use a defined preprocessor constant:
#ifdef ENABLE_TESTS
// code that you want to run ONLY during tests
#endif
Now when building the code, you can selectively define/un-define this constant in your build process – IDE/makefile/build script/command-line – without needing to edit the code:
$ gcc -DENABLE_TESTS source.c
I’ve added this answer to counter-balance all of the early #if 0 answers, but this construct from the accepted answer is the best answer to the specific question: /**/ foo(); /*/ bar(); /**/. Please use such comment tricks sparingly.