This patch adds tests for the "NewImage" attribute in Alternator Streams in NEW_IMAGE and NEW_AND_OLD_IMAGES mode. It reproduces issue #7107, that items' key attributes are missing in the NewImage. It also verifies the risky corner cases where the new item is "empty" and NewImage should include just the key, vs. the case where the item is deleted, so NewImage should be missing. This test currently passes on AWS DynamoDB, and xfails on Alternator. Refs #7107. Signed-off-by: Nadav Har'El <nyh@scylladb.com> Message-Id: <20200825113857.106489-1-nyh@scylladb.com>