[test] Print diagnostic message on failure in test-gc.cc

Making test failures more convenient to debug than simply failing
a .ToHandleChecked() call.

Change-Id: Ieb4553bec8886d1a4eb0dbf0c7bc53ac6435a82c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2412528
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69928}

test/cctest/wasm/test-gc.cc

@@ -1059,10 +1059,20 @@ TEST(JsAccess) {
   isolate->clear_pending_exception();
 
   maybe_result = tester.CallExportedFunction("producer", 0, nullptr);
+  if (maybe_result.is_null()) {
+    FATAL("Calling 'producer' failed: %s",
+          *v8::String::Utf8Value(reinterpret_cast<v8::Isolate*>(isolate),
+                                 try_catch.Message()->Get()));
+  }
   {
     Handle<Object> args[] = {maybe_result.ToHandleChecked()};
     maybe_result = tester.CallExportedFunction("consumer", 1, args);
   }
+  if (maybe_result.is_null()) {
+    FATAL("Calling 'consumer' failed: %s",
+          *v8::String::Utf8Value(reinterpret_cast<v8::Isolate*>(isolate),
+                                 try_catch.Message()->Get()));
+  }
   Handle<Object> result = maybe_result.ToHandleChecked();
   CHECK(result->IsSmi());
   CHECK_EQ(42, Smi::cast(*result).value());