code: def testMelToHz(self):
      mel = 5
      expected_hz = 700.0 * (math.exp(mel / 1127.01048) - 1.0)
      self.assertAlmostEqual(expected_hz, mel2hz(mel))
  
file_path: essentia/test/src/unittests/base/test_utils.py
imports: from essentia_test import *
  import math
  import cmath
  import sys
label_desc: Use image node_id 13 for calling the TestUtils obj's underlying member method code with example usage: obj.testMelToHz() without return types