What tests are made of.
C Python Makefile
Latest commit 7fed323 Jun 30, 2015 @vmg Merge pull request #72 from ethomson/chdir_warnings
sandbox: check chdir return code


Come out and Clar

In Catalan, "clar" means clear, easy to perceive. Using clar will make it easy to test and make clear the quality of your code.

Historical note

Originally the clar project was named "clay" because the word "test" has its roots in the latin word "testum", meaning "earthen pot", and "testa", meaning "piece of burned clay"?

This is because historically, testing implied melting metal in a pot to check its quality. Clay is what tests are made of.

Quick Usage Overview

Clar is a minimal C unit testing framework. It's been written to replace the old framework in libgit2, but it's both very versatile and straightforward to use.

Can you count to funk?

  • Zero: Initialize test directory

    $ mkdir tests
    $ cp -r $CLAR_ROOT/clar* tests
    $ cp $CLAR_ROOT/test/clar_test.h tests
    $ cp $CLAR_ROOT/test/main.c.sample tests/main.c
  • One: Write some tests

    File: tests/adding.c:

    /* adding.c for the "Adding" suite */
    #include "clar.h"
    static int *answer;
    void test_adding__initialize(void)
        answer = malloc(sizeof(int));
        cl_assert_(answer != NULL, "No memory left?");
        *answer = 42;
    void test_adding__cleanup(void)
    void test_adding__make_sure_math_still_works(void)
        cl_assert_(5 > 3, "Five should probably be greater than three");
        cl_assert_(-5 < 2, "Negative numbers are small, I think");
        cl_assert_(*answer == 42, "The universe is doing OK. And the initializer too.");
  • Two: Build the test executable

    $ cd tests
    $ $CLAR_PATH/generate.py .
    Written `clar.suite` (1 suites)
    $ gcc -I. clar.c main.c adding.c -o testit
  • Funk: Funk it.

    $ ./testit

The Clar Test Suite

Writing a test suite is pretty straightforward. Each test suite is a *.c file with a descriptive name: this encourages modularity.

Each test suite has optional initialize and cleanup methods. These methods will be called before and after running each test in the suite, even if such test fails. As a rule of thumb, if a test needs a different initializer or cleanup method than another test in the same module, that means it doesn't belong in that module. Keep that in mind when grouping tests together.

The initialize and cleanup methods have the following syntax, with suitename being the current suite name, e.g. adding for the adding.c suite.

void test_suitename__initialize(void)
    /* init */

void test_suitename__cleanup(void)
    /* cleanup */

These methods are encouraged to use static, global variables to store the state that will be used by all tests inside the suite.

static git_repository *_repository;

void test_status__initialize(void)
    git_repository_open(_repository, STATUS_REPO);

void test_status__cleanup(void)

void test_status__simple_test(void)
    /* do something with _repository */

Writing the actual tests is just as straightforward. Tests have the void test_suitename__test_name(void) signature, and they should not be static. Clar will automatically detect and list them.

Tests are run as they appear on their original suites: they have no return value. A test is considered "passed" if it doesn't raise any errors. Check the "Clar API" section to see the various helper functions to check and raise errors during test execution.

Caution: If you use assertions inside of test_suitename__initialize, make sure that you do not rely on __initialize being completely run inside your test_suitename__cleanup function. Otherwise you might encounter ressource cleanup twice.

How does Clar work?

To use Clar:

  1. copy the Clar boilerplate to your test directory
  2. copy (and probably modify) the sample main.c (from $CLAR_PATH/test/main.c.sample)
  3. run the Clar mixer (a.k.a. generate.py) to scan your test directory and write out the test suite metadata.
  4. compile your test files and the Clar boilerplate into a single test executable
  5. run the executable to test!

The Clar boilerplate gives you a set of useful test assertions and features (like accessing or making sandbox copies of fixture data). It consists of the clar.c and clar.h files, plus the code in the clar/ subdirectory. You should not need to edit these files.

The sample main.c (i.e. $CLAR_PATH/test/main.c.sample) file invokes clar_test(argc, argv) to run the tests. Usually, you will edit this file to perform any framework specific initialization and teardown that you need.

The Clar mixer (generate.py) recursively scans your test directory for any .c files, parses them, and writes the clar.suite file with all of the metadata about your tests. When you build, the clar.suite file is included into clar.c.

The mixer can be run with Python 2.5, 2.6, 2.7, 3.0, 3.1, 3.2 and PyPy 1.6.

Commandline usage of the mixer is as follows:

$ ./generate.py .

Where . is the folder where all the test suites can be found. The mixer will automatically locate all the relevant source files and build the testing metadata. The metadata will be written to clar.suite, in the same folder as all the test suites. This file is included by clar.c and so must be accessible via #include when building the test executable.

$ gcc -I. clar.c main.c suite1.c test2.c -o run_tests

Note that the Clar mixer only needs to be ran when adding new tests to a suite, in order to regenerate the metadata. As a result, the clar.suite file can be checked into version control if you wish to be able to build your test suite without having to re-run the mixer.

This is handy when e.g. generating tests in a local computer, and then building and testing them on an embedded device or a platform where Python is not available.


Clar can create sandboxed fixtures for you to use in your test. You'll need to compile clar.c with an additional CFLAG, -DCLAR_FIXTURE_PATH. This should be an absolute path to your fixtures directory.

Once that's done, you can use the fixture API as defined below.

The Clar API

Clar makes the following methods available from all functions in a test suite.

  • cl_must_pass(call), cl_must_pass_(call, message): Verify that the given function call passes, in the POSIX sense (returns a value greater or equal to 0).

  • cl_must_fail(call), cl_must_fail_(call, message): Verify that the given function call fails, in the POSIX sense (returns a value less than 0).

  • cl_assert(expr), cl_assert_(expr, message): Verify that expr is true.

  • cl_check_pass(call), cl_check_pass_(call, message): Verify that the given function call passes, in the POSIX sense (returns a value greater or equal to 0). If the function call doesn't succeed, a test failure will be logged but the test's execution will continue.

  • cl_check_fail(call), cl_check_fail_(call, message): Verify that the given function call fails, in the POSIX sense (returns a value less than 0). If the function call doesn't fail, a test failure will be logged but the test's execution will continue.

  • cl_check(expr): Verify that expr is true. If expr is not true, a test failure will be logged but the test's execution will continue.

  • cl_fail(message): Fail the current test with the given message.

  • cl_warning(message): Issue a warning. This warning will be logged as a test failure but the test's execution will continue.

  • cl_set_cleanup(void (*cleanup)(void *), void *opaque): Set the cleanup method for a single test. This method will be called with opaque as its argument before the test returns (even if the test has failed). If a global cleanup method is also available, the local cleanup will be called first, and then the global.

  • cl_assert_equal_i(int,int): Verify that two integer values are equal. The advantage of this over a simple cl_assert is that it will format a much nicer error report if the values are not equal.

  • cl_assert_equal_s(const char *,const char *): Verify that two strings are equal. The expected value can also be NULL and this will correctly test for that.

  • cl_fixture_sandbox(const char *): Sets up a sandbox for a fixture so that you can mutate the file directly.

  • cl_fixture_cleanup(const char *): Tears down the previous fixture sandbox.

  • cl_fixture(const char *): Gets the full path to a fixture file.

Please do note that these methods are always available whilst running a test, even when calling auxiliary/static functions inside the same file.

It's strongly encouraged to perform test assertions in auxiliary methods, instead of returning error values. This is considered good Clar style.

Style Example:

 * Bad style: auxiliary functions return an error code

static int check_string(const char *str)
    const char *aux = process_string(str);

    if (aux == NULL)
        return -1;

    return strcmp(my_function(aux), str) == 0 ? 0 : -1;

void test_example__a_test_with_auxiliary_methods(void)
        "String differs after processing"

        "String differs after processing"
 * Good style: auxiliary functions perform assertions

static void check_string(const char *str)
    const char *aux = process_string(str);

        aux != NULL,
        "String processing failed"

        strcmp(my_function(aux), str) == 0,
        "String differs after processing"

void test_example__a_test_with_auxiliary_methods(void)

About Clar

Clar has been written from scratch by Vicent MartĂ­, to replace the old testing framework in libgit2.

Do you know what languages are in on the SF startup scene? Node.js and Latin. Follow @vmg on Twitter to receive more lessons on word etymology. You can be hip too.