.then((activity) => {
assert.isActivity(activity);
assert.isEncryptedActivity(activity);
const fileItem = activity.object.files.items[0];
assert.isFileItem(fileItem);
const thumbnailItem = activity.object.files.items[0].image;
assert.isThumbnailItem(thumbnailItem);
assert.equal(thumbnailItem.width, 640);
assert.isAbove(thumbnailItem.height, 358);
assert.isBelow(thumbnailItem.height, 361);
return spark.internal.conversation.download(activity.object.files.items[0]);
})