heap: add a unit test for malloc(0) and slightly optimize heap_caps_m…

…alloc_prefer

components/heap/heap_caps.c

@@ -259,7 +259,7 @@ IRAM_ATTR void *heap_caps_malloc_prefer( size_t size, size_t num, ... )
     while (num--) {
         caps = va_arg( argp, uint32_t );
         r = heap_caps_malloc_base( size, caps );
-        if (r != NULL) {
+        if (r != NULL || size == 0) {
             break;
         }
     }

components/heap/test/test_malloc.c

@@ -132,3 +132,25 @@ TEST_CASE("malloc(0) should return a NULL pointer", "[heap]")
     p = malloc(0);
     TEST_ASSERT(p == NULL);
 }
+
+static bool failure_occured = false;
+
+static void test_alloc_failure_callback(size_t size, uint32_t caps, const char * function_name)
+{
+    failure_occured = true;
+}
+
+TEST_CASE("malloc/calloc(0) should not call failure callback", "[heap]")
+{
+    void* ptr = NULL;
+    esp_err_t ret = heap_caps_register_failed_alloc_callback(test_alloc_failure_callback);
+    TEST_ASSERT(ret == ESP_OK);
+    ptr = malloc(0);
+    TEST_ASSERT_NULL(ptr);
+    /* Check that our callback was NOT called */
+    TEST_ASSERT_FALSE(failure_occured);
+    /* Do the same thing for calloc */
+    ptr = calloc(0, 0);
+    TEST_ASSERT_NULL(ptr);
+    TEST_ASSERT_FALSE(failure_occured);
+}