fixup! test: avoid dangling FFI string pointer

Author: trivikr

test/ffi/fixture_library/ffi_test_library.c

@@ -108,8 +108,11 @@ FFI_EXPORT uint8_t string_equals_hello(const char* str) {
   return str && strcmp(str, "hello") == 0;
 }
 
-FFI_EXPORT char* overwrite_string(char* str, int32_t value, uint64_t length) {
-  return memset(str, value, (size_t)length);
+FFI_EXPORT uint8_t overwrite_string(char* str,
+                                    int32_t value,
+                                    uint64_t length) {
+  memset(str, value, (size_t)length);
+  return (uint8_t)str[0];
 }
 
 FFI_EXPORT char* string_concat(const char* a, const char* b) {

test/ffi/test-ffi-fast-buffer.js

@@ -100,15 +100,15 @@ test('fast FFI refreshes cached temporary string buffers', () => {
   const lib = new ffi.DynamicLibrary(libraryPath);
   const overwriteString = lib.getFunction('overwrite_string', {
     arguments: ['string', 'i32', 'u64'],
-    return: 'pointer',
+    return: 'u8',
   });
 
   try {
     const mutated = overwriteString('hello', 0x79, 1n);
-    assert.strictEqual(ffi.toString(mutated), 'yello');
+    assert.strictEqual(mutated, 0x79);
 
     const refreshed = overwriteString('hello', 0x79, 0n);
-    assert.strictEqual(ffi.toString(refreshed), 'hello');
+    assert.strictEqual(refreshed, 0x68);
   } finally {
     lib.close();
   }