code: def test_constructor_loads_from_os_when_not_provided():
      """OutputCredentials - Constructor
  
      When not provided, prefix and aws account id are loaded from the OS Environment.
      """
  
      provider = OutputCredentialsProvider(
          "that_service_name", config=CONFIG, region=REGION
      )
      assert_equal(provider._prefix, "prefix")
      assert_equal(provider.get_aws_account_id(), "123456789012")
  
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 1 for calling a global function with example usage: test_constructor_loads_from_os_when_not_provided() without return types