automl tables batch predict lacks test

[sirtorry]

other tables samples may lack tests as well.

[nnegrey]

If you want an example, Java has tests.
https://github.com/GoogleCloudPlatform/java-docs-samples/tree/master/automl/beta/src/test/java/com/example/automl

[tmatsuo]

@sirtorry Friendly ping