Unit testing C via python

example.c

#include <stdio.h>
#include <string.h>
#include <assert.h>

#define _concat(X, Y) X##Y
#define concat(X, Y) _concat(X, Y)

#ifdef testmode
#define test_(NAME, CTR) \
	const char *concat(_name_test_, CTR) = NAME; \
	const char *concat(_test_, CTR)(void)
#else
#define test_(NAME, CTR) \
	const char *concat(_name_test_, CTR) = NULL; \
	static const char *concat(_test_, CTR)(void)
#endif
#define test(NAME) test_(NAME, __COUNTER__)

char *cpystr(char *dst, const char *src, size_t max)
{
	while (max--) {
		*dst = *(src++);
		if (!*(dst++))
			break;
	}
	return dst;
}
test("cpystr handles max = 0") {
	char dst[1] = {'A'};
	char src[1] = {'B'};
	if (cpystr(dst, src, 0) != dst)
		return "Wrong return value";
	if (dst[0] != 'A')
		return "dst modified";
	return 0;
}
test("cpystr copies shorter src correctly") {
	char dst[5] = "ABCD";
	char src[3] = "XY";
	if (cpystr(dst, src, 0) != dst + 3)
		return "Wrong return value";
	if (memcmp(dst, src, 3))
		return "Mismatch";
	if (dst[4] != 'D')
		return "Tail not preserved";
	return 0;
}

int
main(void)
{
	return 0;
}

Makefile

.PHONY: test
test: example.so
	python test.py ./$<

example: example.c
	$(CC) $(CFLAGS) $(LDFLAGS) $(LDLIBS) -o $@ $<

example.so: example.c
	$(CC) $(CFLAGS) $(LDFLAGS) -shared -Dtestmode -o $@ $<

.PHONY: clean
clean:
	rm -f example.so example

test.py

import subprocess
import sys
import unittest

from ctypes import *

class TestGenerated(unittest.TestCase):
    pass

def get_symbols(libpath):
    output = subprocess.check_output(["nm", "-D", "--defined-only", libpath])
    for line in output.decode().strip().split("\n"):
        _, _, symbol = line.split()
        yield symbol


def make_tests(libpath):
    lib = cdll.LoadLibrary(libpath)

    for symbol in get_symbols(libpath):
        if not symbol.startswith("_test_"):
            continue

        func = getattr(lib, symbol)
        func.restype = c_char_p
        def test(self, f=func):
            r = f()
            if r:
                raise self.failureException(r.decode())

        name_p = c_char_p.in_dll(lib, "_name" + symbol)
        test.__doc__ = name_p.value.decode()

        setattr(TestGenerated, f"test_{symbol[len('_test_'):]}", test)

if __name__ == "__main__":
    make_tests(sys.argv.pop(1))
    unittest.main()