message: tests: Add more move tests
  We now check that appending a child to a moved document performs no
  allocations - this is already the case, but if we neglected to copy the
  allocator state this test would fail.
diff: @@ -1739,4 +1739,15 @@ TEST_XML(document_move_buffer, "<node1/><node2/>")
  CHECK(other.child(STR("node2")).offset_debug() == 9);
  }
  +
  +TEST_XML(document_move_append_child_zero_alloc, "<node1/><node2/>")
  +{
  + test_runner::_memory_fail_threshold = 1;
  +
  + xml_document other = std::move(doc);
  +
  + CHECK(other.append_child(STR("node3")));
  +
  + CHECK_NODE(other, STR("<node1/><node2/><node3/>"));
  +}
  #endif
  