cmocka  0.4.1
cmocka Documentation

This is the online reference for developing with the cmocka library. It documents the cmocka C API.

cmocka is an elegant unit testing framework for C with support for mock objects. It only requires the standard C library, works on a lot of platforms (including embedded) and with different compilers.


Tests written with cmocka are compiled into stand-alone executables and linked with the CMock library, the standard C library and module being tested. Any symbols external to the module being tested should be mocked - replaced with functions that return values determined by the test - within the test application. Even though significant differences may exist between the target execution environment of a code module and the environment used to test the code the unit testing is still valid since its goal is to test the logic of a code modules at a functional level and not necessarily all of its interactions with the target execution environment.

The CMocka library provides:

A cmocka test

Test cases are functions with the signature void function(void **state). Test applications initialize a table with test case function pointers using unit_test() macros. This table is then passed to the run_tests() macro to execute the tests. run_tests() sets up the appropriate exception / signal handlers and other data structures prior to running each test function. When a unit test is complete run_tests() performs various checks to determine whether the test succeeded.

#include <stdarg.h>
#include <stddef.h>
#include <setjmp.h>
#include <cmocka.h>
/* A test case that does nothing and succeeds. */
static void null_test_success(void **state) {
(void) state; /* unused */
int main(void) {
const UnitTest tests[] = {
return run_tests(tests);

Mock objects

You may already have heard the term "Mock Object". It describes a special case of an object that mimics a real instance of an interface in order to provide enough of that interface for testing. While there are several unit testing frameworks that already provide some easy to use interface for creating different kinds of "fake" objects for testing, there may be some confusion in terms of how these test objects are programmed and what the behavioral differences are between them.

Mock objects include some logic and the test driver is able to modify the behaviour and state. The object can call some functions or act on different input (abort a test if it is wrong). The test driver injects what it expects the mock object to return. CMocka provides and API to easily mock code.

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cmocka is not thread safe and it is not the goal of it to be it. However if you use cmocka for writing tests in an application which uses threads, you can set the following envionment variable:

    CMOCKA_TEST_ABORT='1' ./my_threading_test

With this environment variable set to '1', cmocka will call abort() if a test fails. Else it is likely that you will run into deadlocks with mutexes or other funny errors.