docstr: LocalFileDriver - Save and Has Credentials
docstr_tok: ["LocalFileDriver","-","Save","and","Has","Credentials"]
code: def test_save_and_has_credentials(self):
      """LocalFileDriver - Save and Has Credentials"""
      assert_false(self._fs_driver.has_credentials("descriptor"))
  
      credentials = Credentials("aaaa", True)  # pretend it's encrypted
      self._fs_driver.save_credentials("descriptor", credentials)
  
      assert_true(self._fs_driver.has_credentials("descriptor"))
  
imports: import json
  import os
  from collections import OrderedDict
  from botocore.exceptions import ClientError
  from mock import patch, MagicMock
  from moto import mock_kms, mock_ssm
  from nose.tools import assert_equal, assert_false, assert_is_instance, assert_is_none, assert_is_not_none, assert_not_equal, assert_true
  from streamalert.alert_processor.outputs.output_base import OutputProperty
  from streamalert.alert_processor.outputs.credentials.provider import SSMDriver, LocalFileDriver, Credentials, OutputCredentialsProvider, EphemeralUnencryptedDriver, SpooledTempfileDriver, get_formatted_output_credentials_name
  from tests.unit.streamalert.alert_processor import PREFIX, CONFIG, KMS_ALIAS, REGION, MOCK_ENV
  from tests.unit.streamalert.alert_processor.helpers import encrypt_with_kms, setup_mock_kms
label_desc: Use image node_id 3 for calling the TestLocalFileDriver obj's underlying member method code with example usage: obj.test_save_and_has_credentials() without return types