Understanding how hooks work and why you need them

Hooks enable you to set breakpoints. Hooks are instructions that can be inserted into a program by a compiler at compile time. Hooks can be placed at the entrances and exits of blocks, at statement boundaries, and at points in the program where program flow might change between statement boundaries (called path points). If you compile a program with the TEST compiler option and specify any suboption except NONE or NOHOOK, the compiler inserts hooks into your program (except for Enterprise COBOL for z/OS® Version 5, which never generates compiled in hooks).