Made of Bugs

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Check Plus: An EDSL for writing unit tests in C

Check is an excellent unit-testing framework for C code, used by a number of relatively well-known projects. It includes features such as running all tests in separate address spaces (using fork(2)), which means that the test suite can properly report segfaults or similar crashes without the test runner crashes.

My main complaint about Check is that (unsurprisingly for a framework written in C), it’s not very declarative. After you define all your tests as separate functions, you need to write code to manually collect them into “test cases”, which you then collect into “test suites”, which you can then run. While this is an understandable interface for a C library to provide, as a user I found that it rapidly annoyed me, and so I wrote Check Plus.

Check Plus is a simple library I wrote that uses some preprocessor tricks and GNU C extensions to provide a declarative EDSL within C for declaring and collecting your test cases. Check-Plus is a single self-contained header file distributed under the LGPL (like Check), so it should be easy to pull into your project.

Example  🔗︎

Check-Plus lets you declare your Check suites and test cases in a declarative manner. A simple example, shipped with Check-Plus, would look like:

#include <string.h>
#include <stdlib.h>

#include "check-plus.h"

#define SUITE_NAME example
BEGIN_SUITE("Example test suite");

#define TEST_CASE core
BEGIN_TEST_CASE("Core tests");

    fail_unless(strcmp("hello", "HELLO") != 0);
    fail_unless(strcasecmp("hello", "HELLO") == 0);

    char buf[1024] = {0};
    strcat(buf, "Hello, ");
    strcat(buf, "World.");
    fail_unless(strcmp(buf, "Hello, World.") == 0);

#undef TEST_CASE

Having done that, you can extract the declared test suite using construct_test_suite(example), and run it using the standard Check test runner tools.

You can, of course, define multiple test cases within a single suite, and you can even define test fixtures using

DEFINE_FIXTURE(setup, teardown);


The equivalent code, without Check-Plus, would look similar, but instead of the BEGIN_ and END_ blocks to define the suite and test case, you’d have to write something like:

Suite *
example_suite (void)
  Suite *s = suite_create ("Example test suite");

  /* Core test case */
  TCase *tc_core = tcase_create ("Core tests");
  tcase_add_test (tc_core, test_strcmp);
  tcase_add_test (tc_core, test_strcat);
  suite_add_tcase (s, tc_core);

  return s;

It’s not a huge difference, but it’s big enough that I really appreciate it once the test suite gets large. For more documentation on Check, check out its manual.

Let me know if you find this useful for anything. Next week, I’ll do a writeup on the tricks behind the implementation.