diff --git a/scripts/setupJestEnv.ts b/scripts/setupJestEnv.ts
index b7c9982f86392247d4a8440d07713d2051711388..9275b3ab0f9745c96a0ae0abeb60c9e750f5e934 100644
--- a/scripts/setupJestEnv.ts
+++ b/scripts/setupJestEnv.ts
@@ -10,8 +10,9 @@ let instanceId = 1
       invokeSync(args: Record<string, any>, callback: unknown) {
         console.log(`invoke`, JSON.stringify(args))
         if (args.name === 'constructor') {
-          return instanceId++
+          return { type: 'return', params: instanceId++ }
         }
+        return { type: 'return', params: null }
       },
       invokeAsync(args: unknown, callback: unknown) {
         console.log(`invokeAsync`, JSON.stringify(args))