class_docstr: Tests the helper functions for classical pre-processsing.
class_docstr_tok: ["Tests","the","helper","functions","for","classical","pre-processsing","."]
docstr: Tests that the function gray_code generates the proper
  Gray code of given rank.
docstr_tok: ["Tests","that","the","function","gray_code","generates","the","proper","Gray","code","of","given","rank","."]
code: def test_gray_code(self, rank, expected_gray_code):
      """Tests that the function gray_code generates the proper
      Gray code of given rank."""
  
      assert gray_code(rank) == expected_gray_code
  
imports: import pytest
  import numpy
  import pennylane
  from pennylane import numpy
  from pennylane.templates.state_preparations.mottonen import gray_code, _get_alpha_y
label_desc: Use image node_id 1 for calling the TestHelpers obj's underlying member method code with example usage: obj.test_gray_code(rank, expected_gray_code) without return types