code: def test_preemphasis(coef, zi, return_zf: bool, dtype):
      x = np.arange(10, dtype=dtype)
  
      if return_zf:
          y, zf = librosa.effects.preemphasis(
              x, coef=coef, zi=zi, return_zf=return_zf
          )
      else:
          y = librosa.effects.preemphasis(
              x, coef=coef, zi=zi, return_zf=return_zf
          )
  
      assert np.allclose(y[1:], x[1:] - coef * x[:-1])
      assert x.dtype == y.dtype
  
imports: import warnings
  import os
  from contextlib import nullcontext
  import numpy
  import pytest
  import librosa
label_desc: Use image node_id 20 for calling a global function with example usage: test_preemphasis(coef, zi, return_zf, dtype) without return types