Add tests to check "freed memory fill" behaviour in debug mode

test/test-api-fill.c

@@ -15,6 +15,7 @@ terms of the MIT license. A copy of the license can be found in the file
 bool check_zero_init(uint8_t* p, size_t size);
 #if MI_DEBUG >= 2
 bool check_debug_fill_uninit(uint8_t* p, size_t size);
+bool check_debug_fill_freed(uint8_t* p, size_t size);
 #endif
 
 // ---------------------------------------------------------------------------
@@ -269,6 +270,22 @@ int main(void) {
     result &= check_debug_fill_uninit(p, malloc_size);
     mi_free(p);
   });
+
+
+  CHECK_BODY("fill-freed-small", {
+    size_t malloc_size = MI_SMALL_SIZE_MAX / 2;
+    uint8_t* p = (uint8_t*)mi_malloc(malloc_size);
+    mi_free(p);
+    // First sizeof(void*) bytes will contain housekeeping data, skip these
+    result = check_debug_fill_freed(p + sizeof(void*), malloc_size - sizeof(void*));
+  });
+  CHECK_BODY("fill-freed-large", {
+    size_t malloc_size = MI_SMALL_SIZE_MAX * 2;
+    uint8_t* p = (uint8_t*)mi_malloc(malloc_size);
+    mi_free(p);
+    // First sizeof(void*) bytes will contain housekeeping data, skip these
+    result = check_debug_fill_freed(p + sizeof(void*), malloc_size - sizeof(void*));
+  });
 #endif
 
   // ---------------------------------------------------
@@ -301,4 +318,15 @@ bool check_debug_fill_uninit(uint8_t* p, size_t size) {
   }
   return result;
 }
+
+bool check_debug_fill_freed(uint8_t* p, size_t size) {
+  if(!p)
+    return false;
+
+  bool result = true;
+  for (size_t i = 0; i < size; ++i) {
+    result &= p[i] == MI_DEBUG_FREED;
+  }
+  return result;
+}
 #endif