code: def mel_to_spec(self):
      mel_basis = np_transforms.build_mel_basis(**self.config)
      mel = np.random.rand(self.config.num_mels, 20)  # [C, T]
      spec = np_transforms.mel_to_spec(mel=mel, mel_basis=mel_basis)
      self.assertEqual(spec.shape, (self.config.fft_size // 2 + 1, 20))
  
imports: import math
  import os
  import unittest
  from dataclasses import dataclass
  import librosa
  import numpy
  from coqpit import Coqpit
  from tests import get_tests_input_path, get_tests_output_path, get_tests_path
  from TTS.utils.audio import numpy_transforms
label_desc: Use image node_id 7 for calling the TestNumpyTransforms obj's underlying member method code with example usage: obj.mel_to_spec() without return types