code: def _validate(wdl_file):
      
      start_dir = os.getcwd()
      os.chdir(os.path.dirname(wdl_file))
      print("Validating", wdl_file)
      subprocess.check_call(["wdltool", "validate", wdl_file])
      os.chdir(start_dir)
docs: Run validation on the generated WDL output using wdltool.