A crash-course of using Cmocka

The use of Cmocka is deprecated. A better choice is to use Cmock (http://www.throwtheswitch.org/cmock) and (http://www.throwtheswitch.org/ceedling).

Unit testing is not just value validation using assertions. An important testing technique, namely mock, should be equally addressed. Cmocka provides a test framework of conducting mock features. The following content serves as a summary of two related links (https://blog.microjoe.org/2017/unit-tests-c-cmocka-coverage-cmake.html#assert-functions and https://lwn.net/Articles/558106/), targeting to clarify the concept of mock and the usage of Cmocka.

It is assumed that users are able to generate dynamically libraries of Cmocka. The test platform is on a Ubuntu. Unfortunately, LLVM on MacOS does not recognize –wrap option. Following the steps below to complete source code preparation:

  1. Download the source from https://cmocka.org/files/1.1/. Decompress the folder.

  2. Enter the decompressed folder and follow the commands above to build the source code. Line 3 (i.e., cmake ..) might be overlooked from time to time. Usally ‘..’ points to where cmocka is.

$ mkdir build
$ cd build
$ cmake ..
$ make clean
$ make -j4

  1. To show how the library to be integrated into your project, we use the chef_wrap example that comes with the cmocka package. Copy the chef_wrap folder from Cmocka example into a preferred path.

  2. Create a folder and name it as lib under chef_wrap folder. And copy the dynamic library (under the path build/src/) into the lib folder. You should be able to see three files (libcmocka.so.0.4.1, libcmocka.s0.0 and libcmocka.so) under the lib folder. Two of the files are symbolic links, and they are related to the so file as below. One could create the symbolic links if not exist.

lrwxrwxrwx 1    14 Sep 22 22:07 libcmocka.so -> libcmocka.so.0
lrwxrwxrwx 1    18 Sep 22 22:07 libcmocka.so.0 -> libcmocka.so.0.4.1
-rwxr-xr-x 1 52768 Sep 22 22:07 libcmocka.so.0.4.1

Virtual box shared folder does not allow symbolic links to be created (nor exist). Hence use a folder other than the shared ones.

  1. Modify chef.c and waiter_test_wrap.c. Change #include <cmocka.h> to #include “cmocka.h”.

  2. Copy cmocka.h (under include folder) under the chef_wrap folder.

  3. Create a shell script to compile and link the source code. An example of such a script could be the following:

# System variables.
SYSTEM=$(uname)
CC=gcc
LD=gcc

SRC_DIR=./
INC_DIR=./
LIB_DIR=./

# Compile src files.
$CC -Wall -c $SRC_DIR/chef.c -I$INC_DIR -o $SRC_DIR/chef.o
$CC -Wall -c $SRC_DIR/waiter_test_wrap.c -I$INC_DIR -o $SRC_DIR/waiter_test_wrap.o

# Link objs.
$LD $SRC_DIR/chef.o $SRC_DIR/waiter_test_wrap.o -o $SRC_DIR/chef_test -L./$LIB_DIR -lcmocka -Wl,-rpath=./$LIB_DIR

  1. The execution result is as follows:

[==========] Running 2 test(s).
[ RUN      ] test_order_hotdog
Chef couldn't cook hotdog: Unknown error!
[  ERROR   ] --- 0xffffffffffffffff != 0
[   LINE   ] --- .//waiter_test_wrap.c:130: error: Failure!
[  FAILED  ] test_order_hotdog
[ RUN      ] test_bad_dish
Chef couldn't cook hotdog: Unknown error!
[  ERROR   ] --- 0xffffffffffffffff != 0xfffffffffffffffe
[   LINE   ] --- .//waiter_test_wrap.c:163: error: Failure!
[  FAILED  ] test_bad_dish
[==========] 2 test(s) run.
[  PASSED  ] 0 test(s).
[  FAILED  ] 2 test(s), listed below:
[  FAILED  ] test_order_hotdog
[  FAILED  ] test_bad_dish

2 FAILED TEST(S)