mocking

To mock external dependencies in C unit tests, you introduce wrapper.h and wrapper.c files, replace direct library calls with wrappers, and override weak symbols in test files to simulate specific behaviors or failures deterministically.

The MOCKABLE pattern for mocking POSIX and C stdlib calls provides zero-overhead wrappers using weak symbol overrides in debug builds, allowing test files to substitute mock implementations without modifying production code.

Yes, you can use weak symbols to test curl, talloc, and yyjson libraries by replacing direct calls with wrappers from wrapper.c and overriding them in your test files to simulate failures or specific behaviors during CI runs.

You simulate open, read, and write failures in hermetic C tests by replacing direct system calls with wrappers and overriding the weak symbols in your test files to inject mock implementations that return failure conditions.

Mocking external dependencies with wrappers requires replacing direct calls with wrappers in production code, but the weak symbol override mechanism ensures that test mock implementations inject behavior changes without altering the production logic itself.

A limitation of using weak symbols for mocking C dependencies is that you must replace direct calls with wrappers across your codebase, requiring modifications to existing source files to enable test overrides and deterministic behavior.