How to use the tftest.__init__.TerraformTestError function in tftest

def execute_command(self, cmd, *cmd_args):
    """Run arbitrary Terraform command."""
    _LOGGER.debug([cmd, cmd_args])
    cmdline = [self.terraform, cmd]
    cmdline += cmd_args
    p = subprocess.Popen(cmdline, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                         cwd=self.tfdir, env=os.environ.copy())
    out, err = p.communicate()
    out = out.decode('utf-8', errors='ignore')
    err = err.decode('utf-8', errors='ignore')
    retcode = p.returncode
    if retcode == 1:
      message = 'Error running command {command}: {retcode} {out} {err}'.format(
          command=cmd, retcode=retcode, out=out, err=err)
      _LOGGER.critical(message)
      raise TerraformTestError(message)
    return TerraformCommandOutput(retcode, out, err)

Args:
      tf_vars: the Terraform variables to use for plan/apply/destroy
      plan: run plan
      output: run output
      destroy: run destroy if apply raises an error

    Returns:
      Wrapped output if output is run from here.
    """
    if plan:
      self.plan(tf_vars=tf_vars)
    # catch errors so we can run destroy before re-raising
    try:
      self.apply(tf_vars=tf_vars)
    except TerraformTestError:
      if destroy:
        _LOGGER.warn('running teardown to clean up')
        self.teardown(tf_vars)
      raise
    if output:
      return self.output()