You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: relation_test.rb
    path of file: ./repos/openstreetmap-website/test/models
    
    the code of the file until where you have to start completion: require "test_helper"

class RelationTest < ActiveSupport::TestCase
  def test_from_xml_no_id
    noid = "<osm><relation version='12' changeset='23' /></osm>"
    assert_nothing_raised do
      Relation.from_xml(noid, :create => true)
    end
    message = assert_raise(OSM::APIBadXMLError) do
      Relation.from_xml(noid, :create => false)
    end
    assert_match(/ID is required when updating/, message.message)
  end

  def test_from_xml_no_changeset_id
    nocs = "<osm><relation id='123' version='12' /></osm>"
    message_create = assert_raise(OSM::APIBadXMLError) do
      Relation.from_xml(nocs, :create => true)
    end
    assert_match(/Changeset id is missing/, message_create.message)
    message_update = assert_raise(OSM::APIBadXMLError) do
      Relation.from_xml(nocs, :create => false)
    end
    assert_match(/Changeset
    
  def test_relation_members
    relation = create(:relation)
    node = create(:node)
    way = create(:way)
    other_relation = create(:relation)
    create(:relation_member, :relation => relation, :member => node, :member_role => "some node")
    create(:relation_member, :relation => relation, :member => way, :member_role => "some way")
    create(:relation_member, :relation => relation, :member => other_relation, :member_role => "some relation")

    members = Relation.find(relation.id).relation_members
    assert_equal 3, members.count
    assert_equal "some node", members[0].member_role
    assert_equal "Node", members[0].member_type
    assert_equal node.id, members[0].member_id
    assert_equal "some way", members[1].member_role
    assert_equal "Way", members[1].member_type
    assert_equal way.id, members[1].member_id
    assert_equal "some relation", members[2].member_role
    assert_equal "Relation", members[2].member_type
    assert_equal other_relation.id, members[2].member_id
  end