tests: add build time option for emulating malloc(0) behavior

Allow to override malloc/calloc functions to provide a version that
behaves like esp-idf one, when malloc(0) is called.

Signed-off-by: Davide Bettio <davide@uninstall.it>

tests/test.c

@@ -75,6 +75,34 @@ struct Test
 #define SKIP_STACKTRACES false
 #endif
 
+#include <malloc.h>
+
+// Enabling this will override malloc and calloc weak symbols,
+// so we can force an alternative version of malloc that returns
+// NULL when size is 0.
+// This is useful to find debugging or finding some kind of issues.
+#ifdef FORCE_MALLOC_ZERO_RETURNS_NULL
+void *malloc(size_t size)
+{
+    if (size == 0) {
+        return 0;
+    } else {
+        return memalign(sizeof(void *), size);
+    }
+}
+
+void *calloc(size_t nmemb, size_t size)
+{
+    if (size == 0) {
+        return 0;
+    } else {
+        void *ptr = memalign(sizeof(void *), nmemb * size);
+        memset(ptr, 0, nmemb * size);
+        return ptr;
+    }
+}
+#endif
+
 struct Test tests[] = {
     TEST_CASE_EXPECTED(add, 17),
     TEST_CASE_EXPECTED(fact, 120),