testSubscription will return a TestSubscriptionPayload which is more likely to contain mutation, node, previousValue, and updatedFields, which you can use to update your query. If mutation returns CREATED than the test data will be in node.

There is no

test

subscription in prisma. Can you check if you can do

subscription{
  test{
    node {id}
  }
}

in your prisma demo playground? Also

TestSubscriptionPayload

should be required IMO.