This folder contains functionally identical apps that each receive email messages and log information about them. They each send email messages as well. The apps are written using three different web frameworks: Flask, Django, and the App Engine bundled services wsgi functionality.

When run in App Engine, a GET request to the home page (/ path) will display a page with a form for entering an email address and a text message. When the form is submitted, the app will send a message with that text to the specified address.

You can send a message to an address associated with the app (in the form somename@[CLOUD_PROJECT_ID].appspotmail.com, where CLOUD_PROJECT_ID is the project ID the app is running in, and somename can be any name you'd like) and later view the received message in the log. Or you can send to a nonexistent address such as nobody@example.com and then view the bounced message in the log.

In order to receive incoming email, the app.yaml file must specify mail and mail_bounce as inbound_services.

Deploy this app to App Engine via gcloud app deploy. More about App Engine Bundled Mail API at: https://cloud.google.com/appengine/docs/standard/python3/services/mail#python-3-flask

The App Engine bundled services can be used from within properly configured App Engine applications, and email messages are delivered to those applications, so testing these apps requires deploying them to App Engine.

Each version of the app includes a test program that will:

1. Launch a new version of the app to App Engine without routing network requests to it.
2. Interact with the launched app via web requests to the URL of the specific version that was launched.
3. Examine the log messages of that version to see that the expected actions worked and were logged.
4. Delete the newly launched app version. This is possible because it did not have requests routed to it.

Since each test uses a separate version and addresses test messages and web requests to that version, multiple tests can run simultaneously without interfering with each other.

Bounce notifications will be delivered only to the default App Engine version that has requests routed to it. This means that they will never be delivered to the temporary versions that the test code creates, and would have to be tested another way, such as manually.