ATF-C(3)

💖 ATF-C(3) 💖

okay so bestie, this is the ATF-C(3) page from the Library Functions Manual, and it’s literally the C API for writing ATF-based test programs. Think of it as your group chat for tests: you define test cases, register them, assert stuff, and let the library run main() for you. No cap.

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🌸 NAME 🌸

atf-c — the C API to write ATF-based test programs. The whole squad of macros/functions on this page:

• Assertions that check and can keep going: ATF_CHECK, ATF_CHECK_MSG, ATF_CHECK_EQ, ATF_CHECK_EQ_MSG, ATF_CHECK_MATCH, ATF_CHECK_MATCH_MSG, ATF_CHECK_STREQ, ATF_CHECK_STREQ_MSG, ATF_CHECK_INTEQ, ATF_CHECK_INTEQ_MSG, ATF_CHECK_ERRNO
• Assertions that require and bail if not true: ATF_REQUIRE, ATF_REQUIRE_MSG, ATF_REQUIRE_EQ, ATF_REQUIRE_EQ_MSG, ATF_REQUIRE_MATCH, ATF_REQUIRE_MATCH_MSG, ATF_REQUIRE_STREQ, ATF_REQUIRE_STREQ_MSG, ATF_REQUIRE_INTEQ, ATF_REQUIRE_INTEQ_MSG, ATF_REQUIRE_ERRNO
• Test case definition/registration: ATF_TC, ATF_TC_BODY, ATF_TC_BODY_NAME, ATF_TC_CLEANUP, ATF_TC_CLEANUP_NAME, ATF_TC_HEAD, ATF_TC_HEAD_NAME, ATF_TC_NAME, ATF_TC_WITH_CLEANUP, ATF_TC_WITHOUT_HEAD, ATF_TP_ADD_TC, ATF_TP_ADD_TCS
• Config variable getters: atf_tc_get_config_var, atf_tc_get_config_var_wd, atf_tc_get_config_var_as_bool, atf_tc_get_config_var_as_bool_wd, atf_tc_get_config_var_as_long, atf_tc_get_config_var_as_long_wd
• Result/expectation/control: atf_no_error, atf_tc_expect_death, atf_tc_expect_exit, atf_tc_expect_fail, atf_tc_expect_pass, atf_tc_expect_signal, atf_tc_expect_timeout, atf_tc_fail, atf_tc_fail_nonfatal, atf_tc_pass, atf_tc_require_kmod, atf_tc_require_prog, atf_tc_skip
• Utility helpers: atf_utils_cat_file, atf_utils_compare_file, atf_utils_copy_file, atf_utils_create_file, atf_utils_file_exists, atf_utils_fork, atf_utils_free_charpp, atf_utils_grep_file, atf_utils_grep_string, atf_utils_readline, atf_utils_redirect, atf_utils_wait

---

✨ SYNOPSIS ✨

#include <atf-c.h>

ATF_CHECK(expression);

ATF_CHECK_MSG(expression, fail_msg_fmt, ...);

ATF_CHECK_EQ(expected_expression, actual_expression);

ATF_CHECK_EQ_MSG(expected_expression, actual_expression, fail_msg_fmt,
    ...);

ATF_CHECK_MATCH(regexp, string);

ATF_CHECK_MATCH_MSG(regexp, string, fail_msg_fmt, ...);

ATF_CHECK_STREQ(expected_string, actual_string);

ATF_CHECK_STREQ_MSG(expected_string, actual_string, fail_msg_fmt, ...);

ATF_CHECK_INTEQ(expected_int, actual_int);

ATF_CHECK_INTEQ_MSG(expected_int, actual_int, fail_msg_fmt, ...);

ATF_CHECK_ERRNO(expected_errno, bool_expression);

ATF_REQUIRE(expression);

ATF_REQUIRE_MSG(expression, fail_msg_fmt, ...);

ATF_REQUIRE_EQ(expected_expression, actual_expression);

ATF_REQUIRE_EQ_MSG(expected_expression, actual_expression, fail_msg_fmt,
    ...);

ATF_REQUIRE_MATCH(regexp, string);

ATF_REQUIRE_MATCH_MSG(regexp, string, fail_msg_fmt, ...);

ATF_REQUIRE_STREQ(expected_string, actual_string);

ATF_REQUIRE_STREQ_MSG(expected_string, actual_string, fail_msg_fmt,
    ...);

ATF_REQUIRE_INTEQ(expected_int, actual_int);

ATF_REQUIRE_INTEQ_MSG(expected_int, actual_int, fail_msg_fmt, ...);

ATF_REQUIRE_ERRNO(expected_errno, bool_expression);

ATF_TC(name);

ATF_TC_BODY(name, tc);

ATF_TC_BODY_NAME(name);

ATF_TC_CLEANUP(name, tc);

ATF_TC_CLEANUP_NAME(name);

ATF_TC_HEAD(name, tc);

ATF_TC_HEAD_NAME(name);

ATF_TC_NAME(name);

ATF_TC_WITH_CLEANUP(name);

ATF_TC_WITHOUT_HEAD(name);

ATF_TP_ADD_TC(tp_name, tc_name);

ATF_TP_ADD_TCS(tp_name);

const char*
atf_tc_get_config_var(const atf_tc_t *tc, const char *name);

const char*
atf_tc_get_config_var_wd(const atf_tc_t *tc, const char *name,
    const char *defval);

bool
atf_tc_get_config_var_as_bool(const atf_tc_t *tc, const char *name);

bool
atf_tc_get_config_var_as_bool_wd(const atf_tc_t *tc, const char *name,
    const bool defval);

long
atf_tc_get_config_var_as_long(const atf_tc_t *tc, const char *name);

long
atf_tc_get_config_var_as_long_wd(const atf_tc_t *tc, const char *name,
    const long defval);

void
atf_no_error(void);

void
atf_tc_expect_death(const char *reason, ...);

void
atf_tc_expect_exit(const int exitcode, const char *reason, ...);

void
atf_tc_expect_fail(const char *reason, ...);

void
atf_tc_expect_pass(void);

void
atf_tc_expect_signal(const int signo, const char *reason, ...);

void
atf_tc_expect_timeout(const char *reason, ...);

void
atf_tc_fail(const char *reason);

void
atf_tc_fail_nonfatal(const char *reason);

void
atf_tc_pass(void);

void
atf_tc_require_kmod(const char *kmod);

void
atf_tc_require_prog(const char *prog);

void
atf_tc_skip(const char *reason);

void
atf_utils_cat_file(const char *file, const char *prefix);

bool
atf_utils_compare_file(const char *file, const char *contents);

void
atf_utils_copy_file(const char *source, const char *destination);

void
atf_utils_create_file(const char *file, const char *contents, ...);

void
atf_utils_file_exists(const char *file);

pid_t
atf_utils_fork(void);

void
atf_utils_free_charpp(char **argv);

bool
atf_utils_grep_file(const char *regexp, const char *file, ...);

bool
atf_utils_grep_string(const char *regexp, const char *str, ...);

char *
atf_utils_readline(int fd);

void
atf_utils_redirect(const int fd, const char *file);

void
atf_utils_wait(const pid_t pid, const int expected_exit_status,
    const char *expected_stdout, const char *expected_stderr);

---

💅 DESCRIPTION 💅

ATF gives you a C programming interface to implement test programs. C-based test programs follow this template:

... C-specific includes go here ...

#include <atf-c.h>

ATF_TC(tc1);
ATF_TC_HEAD(tc1, tc)
{
    ... first test case's header ...
}
ATF_TC_BODY(tc1, tc)
{
    ... first test case's body ...
}

ATF_TC_WITH_CLEANUP(tc2);
ATF_TC_HEAD(tc2, tc)
{
    ... second test case's header ...
}
ATF_TC_BODY(tc2, tc)
{
    ... second test case's body ...
}
ATF_TC_CLEANUP(tc2, tc)
{
    ... second test case's cleanup ...
}

ATF_TC_WITHOUT_HEAD(tc3);
ATF_TC_BODY(tc3, tc)
{
    ... third test case's body ...
}

... additional test cases ...

ATF_TP_ADD_TCS(tp)
{
    ATF_TP_ADD_TC(tcs, tc1);
    ATF_TP_ADD_TC(tcs, tc2);
    ATF_TP_ADD_TC(tcs, tc3);
    ... add additional test cases ...

    return atf_no_error();
}

🎀 Definition of test cases 🎀

Test cases have an identifier and are made of three different parts: the header, the body, and an optional cleanup routine, all described in atf-test-case(4). To define test cases, use ATF_TC(), ATF_TC_WITH_CLEANUP(), or ATF_TC_WITHOUT_HEAD(), each taking a single parameter that specifies the test case’s name.

• ATF_TC() wants you to define a header and a body for the test case.
• ATF_TC_WITH_CLEANUP() wants you to define a header, a body, and a cleanup for the test case.
• ATF_TC_WITHOUT_HEAD() wants only a body for the test case.

Important vibe check: these macros do not set the test case up for execution when the program is run. For that, you need later registration with the ATF_TP_ADD_TC() macro, detailed in “Program initialization”.

After that, you define the three parts of the body using three functions. Their headers are given by the ATF_TC_HEAD(), ATF_TC_BODY(), and ATF_TC_CLEANUP() macros, all of which take the test case name you passed to ATF_TC(), ATF_TC_WITH_CLEANUP(), or ATF_TC_WITHOUT_HEAD() and the name of the variable that will hold a pointer to the test case data. After each of these, a block of code is expected, surrounded by opening and closing brackets.

🚀 Program initialization 🚀

The library gives you an easy way to define the test program’s main() function. You should never define one on your own — rely on the library to do it for you. This is done with the ATF_TP_ADD_TCS() macro, which is passed the name of the object that will hold the test cases, i.e., the test program instance. That name can be whatever you want as long as it’s a valid variable identifier.

After the macro, you provide the body of a function, which should only use the ATF_TP_ADD_TC() macro to register the test cases the test program will execute, and return a success error code. The first parameter of this macro matches the name you provided in the former call. You can return the success status using the atf_no_error() function.

🧚 Header definitions 🧚

The test case’s header can define meta-data by using the atf_tc_set_md_var() method, which takes three parameters: the first points to the test case data, the second specifies the meta-data variable to be set, and the third specifies its value. The variable name and value are both strings.

🍓 Configuration variables 🍓

The test case has read-only access to the current configuration variables by means of the bool atf_tc_has_config_var(), const char * atf_tc_get_config_var(), const char * atf_tc_get_config_var_wd(), bool atf_tc_get_config_var_as_bool(), bool atf_tc_get_config_var_as_bool_wd(), long atf_tc_get_config_var_as_long(), and the long atf_tc_get_config_var_as_long_wd() functions, which can be called in any of the three parts of a test case.

The _wd variants take a default value for the variable, returned if the variable is not defined. The other functions without the _wd suffix require the variable to be defined.

🦋 Access to the source directory 🦋

You can get the path to the test case’s source directory from any of its three components by querying the srcdir configuration variable.

🔥 Requiring kernel modules 🔥

Aside from the require.kmods meta-data variable available in the header only, you can also check for additional kernel modules in the test case’s body by using the atf_tc_require_kmod() function, which takes the name of a single kernel module. If it is not found, the test case will be automatically skipped.

🌈 Requiring programs 🌈

Aside from the require.progs meta-data variable available in the header only, you can also check for additional programs in the test case’s body by using the atf_tc_require_prog() function, which takes the base name or full path of a single binary. Relative paths are forbidden. If it is not found, the test case will be automatically skipped.

👑 Test case finalization 👑

The test case finalizes either when the body reaches its end — at which point the test is assumed to have passed, unless any non-fatal errors were raised using atf_tc_fail_nonfatal() — or at any explicit call to atf_tc_pass(), atf_tc_fail(), or atf_tc_skip(). These three functions terminate the execution of the test case immediately. The cleanup routine will be processed afterwards in a completely automated way, regardless of the test case’s termination reason.

• atf_tc_pass() — takes literally zero parameters. No args, no nothing. It just… passes. Iconic behavior honestly 💅
• atf_tc_fail(), atf_tc_fail_nonfatal() and atf_tc_skip() — these besties take a format string plus a variable list of parameters, and those describe, in a user-friendly manner, why the test case failed (or was skipped, respectively). Please give a clear error message in both cases — it's genuinely important so the user can quickly know why the test didn't pass. Nobody wants to play detective at 2am 🔍😭

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🦋 Expectations 🦋

Okay so everything explained in the previous section changes when the test case expectations get redefined by the programmer. Plot twist energy.

Each test case has an internal state called expect that describes what the test case expectations are at any point in time. The value of this property can change during execution by any of these:

• atf_tc_expect_death(reason, ...) — expects the test case to exit prematurely, regardless of the nature of the exit. Just… gone. 💀
• atf_tc_expect_exit(exitcode, reason, ...) — expects the test case to exit cleanly. If exitcode is not -1, the runtime engine will validate that the exit code of the test case matches the one provided in this call. Otherwise, the exact value gets ignored.
• atf_tc_expect_fail(reason, ...) — any failure (fatal or non-fatal, both) raised in this mode is recorded. But those failures do not report the test case as failed — instead the test case finalizes cleanly and is reported as ‘expected failure’, and that report includes the provided reason as part of it. If no error is raised while running in this mode, then the test case is reported as ‘failed’. Yes, success is failure here. We love a paradox 🌀

This mode is lowkey useful for reproducing actual known bugs in tests. Whenever the developer fixes the bug later on, the test case will start reporting a failure, signaling the developer that the test case must be adjusted to the new conditions. In this situation it's useful, for example, to set reason as the bug number for tracking purposes. iykyk 🎀

• atf_tc_expect_pass() — this is the normal mode of execution. In this mode, any failure is reported as such to the user and the test case is marked as ‘failed’. Back to our regularly scheduled programming ✨
• atf_tc_expect_signal(signo, reason, ...) — expects the test case to terminate due to the reception of a signal. If signo is not -1, the runtime engine will validate that the signal that terminated the test case matches the one provided in this call. Otherwise, the exact value will be ignored. 🚨
• atf_tc_expect_timeout(reason, ...) — expects the test case to execute for longer than its timeout. It's giving "running late but make it intentional" ⏰

---

🌸 Helper macros for common checks 🌸

The library provides several macros that are very handy in multiple situations. These basically check some condition after executing a given statement or processing a given expression and, if the condition is not met, they report the test case as failed. Little bodyguards for your tests 🫶

The ‘REQUIRE’ variant of the macros immediately aborts the test case as soon as an error condition is detected, by calling the atf_tc_fail() function. Use this variant whenever it makes no sense to continue the execution of a test case when the checked condition is not met. It's the "nope, we're done here" one 🛑

The ‘CHECK’ variant, on the other hand, reports a failure as soon as it is encountered using the atf_tc_fail_nonfatal() function, but the execution of the test case continues as if nothing had happened. Use this variant whenever the checked condition is important as a result of the test case, but there are other conditions that can be subsequently checked on the same run without aborting. Respect the multitasking queen energy 👑

Additionally, the ‘MSG’ variants take an extra set of parameters to explicitly specify the failure message. This failure message is formatted according to the printf(3) formatters.

• ATF_CHECK(), ATF_CHECK_MSG(), ATF_REQUIRE() and ATF_REQUIRE_MSG() — take an expression and fail if the expression evaluates to false.
• ATF_CHECK_EQ(), ATF_CHECK_EQ_MSG(), ATF_REQUIRE_EQ() and ATF_REQUIRE_EQ_MSG() — take two expressions and fail if the two evaluated values are not equal. The common style is to put the expected value in the first parameter and the observed value in the second parameter. Expected first, observed second, that's the rule 📏
• ATF_CHECK_MATCH(), ATF_CHECK_MATCH_MSG(), ATF_REQUIRE_MATCH() and ATF_REQUIRE_MATCH_MSG() — take a regular expression and a string, and fail if the regular expression does not match the given string. Note that the regular expression is not anchored, so it will match anywhere in the string. Sneaky little thing 🔎
• ATF_CHECK_STREQ(), ATF_CHECK_STREQ_MSG(), ATF_REQUIRE_STREQ() and ATF_REQUIRE_STREQ_MSG() — take two strings and fail if the two are not equal character by character. The common style is to put the expected string in the first parameter and the observed string in the second parameter.
• ATF_CHECK_INTEQ(), ATF_CHECK_INTEQ_MSG(), ATF_REQUIRE_INTEQ() and ATF_REQUIRE_INTQ_MSG() — take two integers and fail if the two are not equal. The common style is to put the expected integer in the first parameter and the observed integer in the second parameter. (And yes, that last one really is spelled ATF_REQUIRE_INTQ_MSG — we copy it with love 🫡)
• ATF_CHECK_ERRNO() and ATF_REQUIRE_ERRNO() — take, first, the error code that the check is expecting to find in the errno variable and, second, a boolean expression that, if it evaluates to true, means that a call failed and errno has to be checked against the first value.

---

🧚 Utility functions 🧚

The following functions are provided as part of the atf-c API to simplify the creation of a variety of tests. In particular, these are useful to write tests for command-line interfaces. CLI testing era fr fr 🖥️✨

• void atf_utils_cat_file(const char *file, const char *prefix) — prints the contents of file to the standard output, prefixing every line with the string in prefix. Spam it with vibes.
• bool atf_utils_compare_file(const char *file, const char *contents) — returns true if the given file matches exactly the expected inlined contents. Exact match or it's a no from me 💅
• void atf_utils_copy_file(const char *source, const char *destination) — copies the file source to destination. The permissions of the file are preserved during the copy. Clingy in the best way 🎀
• void atf_utils_create_file(const char *file, const char *contents, ...) — creates file with the text given in contents, which is a formatting string that uses the rest of the variable arguments. Custom content, zero manual effort ✨
• void atf_utils_file_exists(const char *file) — checks if file exists. Are you there bestie? 👀
• pid_t atf_utils_fork(void) — forks a process and redirects the standard output and standard error of the child to files for later validation with atf_utils_wait(). Fails the test case if the fork fails, so this does not return an error. It's got your back 🫶
• void atf_utils_free_charpp(char **argv) — frees a dynamically-allocated array of dynamically-allocated strings. Clean up your room, bestie 🧹
• bool atf_utils_grep_file(const char *regexp, const char *file, ...) — searches for the regexp, which is a formatting string representing the regular expression, in the file. The variable arguments are used to construct the regular expression. Search party time 🔍
• bool atf_utils_grep_string(const char *regexp, const char *str, ...) — searches for the regexp, which is a formatting string representing the regular expression, in the literal string str. The variable arguments are used to construct the regular expression.
• char * atf_utils_readline(int fd) — reads a line from the file descriptor fd. The line, if any, is returned as a dynamically-allocated buffer that must be released with free(3). If there was nothing to read, returns ‘NULL’. Don't forget the free or it's a leak slay gone wrong 😭
• void atf_utils_redirect(const int fd, const char *file) — redirects the given file descriptor fd to file. This function exits the process in case of an error and does not properly mark the test case as failed. As a result, it should only be used in subprocesses of the test case — especially those spawned by atf_utils_fork(). Read that again, it matters 🚩
• void atf_utils_wait(const pid_t pid, const int expected_exit_status, const char *expected_stdout, const char *expected_stderr) — waits and validates the result of a subprocess spawned with atf_utils_fork(). The validation involves checking that the subprocess exited cleanly and returned the code specified in expected_exit_status, and that its standard output and standard error match the strings given in expected_stdout and expected_stderr. The full vibe check for your child process 👑

If any of the expected_stdout or expected_stderr strings are prefixed with ‘save:’, then they specify the name of the file into which to store the stdout or stderr of the subprocess, and no comparison is performed. Save, not compare — different mode entirely 💾

---

🌈 ENVIRONMENT 🌈

The following variables are recognized by atf-c but should not be overridden other than for testing purposes:

• ATF_BUILD_CC — path to the C compiler.
• ATF_BUILD_CFLAGS — C compiler flags.
• ATF_BUILD_CPP — path to the C/C++ preprocessor.
• ATF_BUILD_CPPFLAGS — C/C++ preprocessor flags.
• ATF_BUILD_CXX — path to the C++ compiler.
• ATF_BUILD_CXXFLAGS — C++ compiler flags.

Leave these alone unless you're literally testing, okay? Respect the environment 🍓

✨ EXAMPLES ✨

okay bestie, this is the part where it all comes together 💖 here's a complete test program with a handful of test cases — it walks you through validating the addition operator, the snprintf function, and open, plus a lil known-bug situation. read it top to bottom, it's giving tutorial but make it iconic 🎀

#include <atf-c.h>

ATF_TC(addition);
ATF_TC_HEAD(addition, tc)
{
    atf_tc_set_md_var(tc, "descr",
                      "Sample tests for the addition operator");
}
ATF_TC_BODY(addition, tc)
{
    ATF_CHECK_EQ(0, 0 + 0);
    ATF_CHECK_EQ(1, 0 + 1);
    ATF_CHECK_EQ(1, 1 + 0);

    ATF_CHECK_EQ(2, 1 + 1);

    ATF_CHECK_EQ(300, 100 + 200);
}

ATF_TC(string_formatting);
ATF_TC_HEAD(string_formatting, tc)
{
    atf_tc_set_md_var(tc, "descr",
                      "Sample tests for the snprintf");
}
ATF_TC_BODY(string_formatting, tc)
{
    char buf[1024];
    snprintf(buf, sizeof(buf), "a %s", "string");
    ATF_CHECK_STREQ_MSG("a string", buf, "%s is not working");
}

ATF_TC(open_failure);
ATF_TC_HEAD(open_failure, tc)
{
    atf_tc_set_md_var(tc, "descr",
                      "Sample tests for the open function");
}
ATF_TC_BODY(open_failure, tc)
{
    ATF_CHECK_ERRNO(ENOENT, open("non-existent", O_RDONLY) == -1);
}

ATF_TC(known_bug);
ATF_TC_HEAD(known_bug, tc)
{
    atf_tc_set_md_var(tc, "descr",
                      "Reproduces a known bug");
}
ATF_TC_BODY(known_bug, tc)
{
    atf_tc_expect_fail("See bug number foo/bar");
    ATF_CHECK_EQ(3, 1 + 1);
    atf_tc_expect_pass();
    ATF_CHECK_EQ(3, 1 + 2);
}

ATF_TP_ADD_TCS(tp)
{
    ATF_TP_ADD_TC(tp, addition);
    ATF_TP_ADD_TC(tp, string_formatting);
    ATF_TP_ADD_TC(tp, open_failure);
    ATF_TP_ADD_TC(tp, known_bug);

    return atf_no_error();
}

---

let's do a lil vibe check on what's happening here, because every one of these is doing something 😌

• the addition test case literally just validates the addition operator — that's it, that's the whole assignment 💅 each ATF_CHECK_EQ drops a pair of values and checks they match, with a couple of blank lines in the body because spacing is self-care.
• string_formatting is out here testing snprintf — it fills buf (a char buf[1024], no less) with "a %s", "string", and then ATF_CHECK_STREQ_MSG compares against "a string" while carrying a custom message, "%s is not working", for when things go sideways 😭
• open_failure proves that opening "non-existent" with O_RDONLY returns -1, and ATF_CHECK_ERRNO makes sure errno is sitting at ENOENT — a whole mood.
• known_bug is the fun one 👀 it calls atf_tc_expect_fail("See bug number foo/bar"), tries the check, then flips back with atf_tc_expect_pass() before its second check. it's literally telling the test "bestie, you're expected to fail here, don't panic."
• and then ATF_TP_ADD_TCS(tp) registers all four test cases with ATF_TP_ADD_TC and returns atf_no_error() — the little happy-ending bow 🎀 on the whole program.

ngl, the ATF_TC, ATF_TC_HEAD and ATF_TC_BODY triple is a lot of boilerplate for one test case, but that's the assignment. every test case gets its own trio. no skipping, no shortcuts, iykyk 🫶

🌈 SEE ALSO 🌈

• atf-test-program(1)
• atf-test-case(4)

---

and that's the whole page, bestie!! 💖 you ate, honestly 👑 this one's from the Debian folks, dated June 12, 2025, and it's the ATF-C(3) manual page — go forth and write some tests that slay ✨🦋🌸