code: def test_approximate_sets():
      """Test the functionality to create approximate set"""
      # Check length of approximated sets with gate depths
      approx_set1, _, _, _ = _approximate_set((), max_length=0)
      approx_set2, _, _, _ = _approximate_set(("t", "h"), max_length=1)
      assert len(approx_set1) == 0
      assert len(approx_set2) == 2
  
      # Verify exist-check reduce redundancy via GP-like summation
      approx_set3, _, _, _ = _approximate_set(
          ("t", "t*", "h"), max_length=3
      )
      approx_set4, _, _, _ = _approximate_set(
          ("t", "t*", "h"), max_length=5
      )
      assert len(approx_set3) == 21  # should be <  39 = 3 + 3x3 + 3x3x3
      assert len(approx_set4) == 84
  
file_path: pennylane/tests/ops/op_math/test_solovay_kitaev.py
imports: import math
  import pytest
  import scipy
  import pennylane
  from pennylane.ops.op_math.decompositions.solovay_kitaev import _SU2_transform, _quaternion_transform, _contains_SU2, _approximate_set, _group_commutator_decompose, sk_decomposition
label_desc: Use image node_id 4 for calling a global function with example usage: test_approximate_sets() without return types