class_docstr: Test statistic holder for Wald-type tests
  
  Parameters
  ----------
  stat : float
      The test statistic
  df : int
      Degree of freedom.
  null : str
      A statement of the test's null hypothesis
  alternative : str
      A statement of the test's alternative hypothesis
  name : str, default "" (empty)
      Name of test
docstr: P-value of test statistic
code: def pval(self) -> float:
      """P-value of test statistic"""
      return 1 - self.dist.cdf(self.stat)
  
file_path: arch/arch/utility/testing.py
imports: from __future__ import annotations
  from functools import cached_property
  from scipy.stats import chi2
label_desc: Use image node_id 3 for calling the WaldTestStatistic obj's underlying member method code with example usage: obj.pval() and returns: unknown