code: def test_tree_space_functions():
      new_tree_space = tree.TreeSpace(1, 1, 0, 1, functions=["SUM"])
  
      assert len(new_tree_space.functions) == 1
  
imports: from opytimizer.core import node
  from opytimizer.spaces import tree
label_desc: Use image node_id 7 for calling a global function with example usage: test_tree_space_functions() without return types