code: def test_FreeGroup_generators():
      assert (x**2 * y**4 * z**-1).contains_generators() == {
          x,
          y,
          z,
      }
      assert (x**-1 * y**3).contains_generators() == {x, y}
  
imports: from sympy.combinatorics.free_groups import free_group, FreeGroup
  from sympy.core import Symbol
  from sympy.testing.pytest import raises
  from sympy.core.numbers import oo
label_desc: Use image node_id 20 for calling a global function with example usage: test_FreeGroup_generators() without return types