Reproduce a scenario in which mongoid does not update if a different _id is provided

mongoid-embeded-doc-update-skipped.rb

require 'mongoid'

Mongoid.configure do |config|
  config.clients.default = {
    hosts: ['localhost:27017'],
    database: 'junk_db',
  }
end

class Contained
  include Mongoid::Document

  embedded_in :container

  field :contained_fld1, type: String
end

class Container
  include Mongoid::Document

  embeds_one :contained

  field :container_fld1, type: String

end

Container.collection.drop
contained = Contained.new(contained_fld1: 'contained_fld1_v1')
container = Container.new(container_fld1: 'container_fld1_v1')
container.contained = contained
container.save

def assert(cond, message = 'assert failed')
  unless cond
    puts Kernel.caller[0...-1].join("\n")
    raise message
  end
end

container = Container.all.first
assert(container.container_fld1 == 'container_fld1_v1')
assert(container.contained.contained_fld1 == 'contained_fld1_v1')

container.update(container_fld1: 'container_fld1_v2', contained: { contained_fld1: 'contained_fld1_v2' })
container = Container.all.first
assert(container.container_fld1 == 'container_fld1_v2')
assert(container.contained.contained_fld1 == 'contained_fld1_v2')

container.update(container_fld1: 'container_fld1_v3', contained: { _id: BSON::ObjectId.new, contained_fld1: 'contained_fld1_v3' })
container = Container.all.first
assert(container.container_fld1 == 'container_fld1_v3')
# the following ka-boom on mongoid 7.3.* and works on mongoid 7.0.12
# reason is [this change](https://github.com/mongodb/mongoid/commit/802277e3e4beba595e805120be56579724a55c60#diff-4be61127029c58a3f70ac4b78d001ef8f28a597f60c4455e43c6e3938d5cc6f3R74-R75) which is a part of https://jira.mongodb.org/browse/MONGOID-4812
# (which seem an unlrelated change but it actually fix a bug that assumed the bson id would be in :id and not in :_id)
#
assert(container.contained.contained_fld1 == 'contained_fld1_v3', ':boom:')