code: def test_flatten():
      dom = Domain({"a": {"b": [0, 1]}, "c": {0, 0.1}})
      assert dom.flatten() == {("a", "b"): [0, 1], ("c",): {0, 0.1}}
  
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 4 for calling a global function with example usage: test_flatten() without return types