code: def test_addition():
      domain_all = Domain(
          {
              "a": [1, 2],
              "b": {"c": {1, 2, 3}, "d": {"o1", "o2"}},
              "e": {3, 4, 5},
          }
      )
      domain_1 = Domain({"a": [1, 2], "b": {"c": {1, 2, 3}}})
      domain_2 = Domain({"b": {"d": {"o1", "o2"}}})
      domain_3 = Domain({"e": {3, 4, 5}})
      assert domain_1 + domain_2 + domain_3 == domain_all
      with pytest.raises(ValueError):
          _ = domain_1 + domain_1
  
file_path: hypertunity/hypertunity/tests/test_domain.py
imports: from collections import namedtuple
  import pytest
  from hypertunity.domain import Domain, DomainNotIterableError, DomainSpecificationError, Sample
label_desc: Use image node_id 5 for calling a global function with example usage: test_addition() without return types