I have been working through AWS learning resources. In several sources, including the AWS doc https://docs.aws.amazon.com/firehose/latest/dev/test-drive-firehose.html, I have seen the "Test with demo data" feature of Kinesis Firehose used to generate test data when learning Kinesis. However, the feature does not appear on the page that the documentation claims. Videos in the Udemy AWS ML Course https://www.udemy.com/course/aws-machine-learning/ also use this "Test with demo data" feature; their UI does not match mine. My question was asked in the course forum as well and has no answer yet.
I have also contacted AWS support and will update when I hear back from them.
The "Test with Demo" option has been removed from the Kinesis Firehouse page. However, AWS has introduced a new way to test your stream. Link below