CUnit - 'Mocking' libc functions - c++

Question

I'm using CUnit for my project unit testing.
I need to test whether I call libc functions with the right parameters & whether I treat their return values the right way.
for example: if I call the bind(...) function - I would like to check which af param I pass & assert if this is the wrong one, and also I would like to emulate it's return value & assert if I check it the right way.
For these purposes I would expect the CUnit environment to have a built-in mechanism to let me call a 'mocked' bind() function while testing and a real bind() function when running the code - but I can't find anything like this.
Can you please tell me if I'm missing something in CUnit, or maybe suggest a way to implement this.
Thanks,
Jo.

Answer 1

Unfortunately, you can't mock functions in C with CUnit.
But you can implement your own mock functions by using and abusing of defines :
Assuming you define UNITTEST when compiling for tests, you can in the tested file (or in a include) define something like this :
#ifdef UNITTEST
#define bind mock_bind
#endif
In a mock_helper.c file that you will compile in test mode :
static int mock_bind_return; // maybe a more complete struct would be usefull here
static int mock_bind_sockfd;
int mock_bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen)
{
CU_ASSERT_EQUAL(sockfd, mock_bind_sockfd);
return mock_bind_return;
}
Then, in your test file :
extern int mock_bind_return;
extern int mock_bind_sockfd;
void test_function_with_bind(void)
{
mock_bind_return = 0;
mock_bind_sockfd = 5;
function_using_bind(mock_bind_sockfd);
}

Answer 2

glibcmock is a solution of mocking libc function with Google Test. for example:
#include "got_hook.h"
#include "gmock/gmock.h"
#include "gtest/gtest.h"
#include <sys/socket.h>
#include <mutex>
#include <memory>
struct MockBind {
MOCK_METHOD3(Bind, int(int, const struct sockaddr*, socklen_t));
};
static MockBind *g_mock{nullptr};
static int Bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen) {
return g_mock->Bind(sockfd, addr, addrlen);
}
static std::mutex g_test_mutex;
TEST(BindTest, MockSample) {
std::lock_guard<std::mutex> lock(g_test_mutex);
std::unique_ptr<MockBind> mock(g_mock = new MockBind());
testing::GotHook got_hook;
ASSERT_NO_FATAL_FAILURE(got_hook.MockFunction("bind", (void*)&Bind));
// ... do your test here, for example:
struct sockaddr* addr = nullptr;
EXPECT_CALL(*g_mock, Bind(1, addr, 20)).WillOnce(testing::Return(0));
EXPECT_EQ(0, bind(1, addr, 20));
}