code: def test_poisson_ppc():
      """
      Tests PPC value
      """
      """
      model = pf.GASLLT(data=data, family=pf.Poisson())
      x = model.fit('BBVI', iterations=100)
      p_value = model.ppc()
      assert(0.0 <= p_value <= 1.0)
      """
  
imports: import numpy
  import pyflux
  import pandas
label_desc: Use image node_id 20 for calling a global function with example usage: test_poisson_ppc() without return types