Proper way to test code with calls to malloc()

[MrMOSFET]

Hi all,

Let's assume I have a C file, with a very simple function:

#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include "code.h"

char *return_str_dup(const char *str)
{
    size_t len = strlen(str);
    char *dup = malloc(len + 1);
    if (dup == NULL) {
        return NULL;
    }
    strncpy(dup, str, len + 1);
    return dup;
}


And I want to write a unit test that checks to make sure the function return NULL if malloc fails (doesn't crash with NULL pointer access).  Is this possible with CppUTest?  I have tried following along with TestMemoryAllocatorTest.cpp without much luck. 

Basically it looks like this:

TEST(tests, test_dup_malloc_fails)
{
    failableMallocAllocator->failAllocNumber(1);
    void *mem = return_str_dup("Why, hello there!");
    POINTERS_EQUAL(NULLPTR, mem);
};

But I can't get malloc to return NULL. 

Any help would be appreciated.  Thanks!

[Bas Vodde]

Hi Mr Mosfet,

In order for the malloc checking to work, you’ll need to ensude the malloc is replace with “cpputest_malloc”

This is usually done by appending a include file that does a #define and declares the cpputest_malloc.

Without that, the mallow call will still like to the stdC malloc and there is no easy way to hijack that.

Thanks,

Bas

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