We can test our Lambda from Greengrass using a test tool from AWS IoT. Click on the Test menu. You should get a form, as shown in the following screenshot. Fill in the subscription topic that we defined while we were deploying Lambda with Greengrass Core:

When done, click on the Subscribe to topic button. Now you should see messages from Raspberry Pi, as shown in the following screenshot:

If you do not see messages from Raspberry Pi, you probably have generated errors while configuring or uploading the Lambda application.