code: def test_basic():
      """Test basic functionality of flatten"""
      d = {"a": {"b": 2, "c": 3}, "c": {"d": 3, "e": 4}}
      assert flatten(d) == {"a.b": 2, "a.c": 3, "c.d": 3, "c.e": 4}
  
label_desc: Use image node_id 1 for calling a global function with example usage: test_basic() without return types