It is my understanding that setting an environment varialbe `TEST_AWS_ACCOUNT_ID` for localstack sets that as the AWS account for the user in localstack.

However, setting it does not actually change any ARNs. For example:

1. Start localstack using `TEST_AWS_ACCOUNT_ID="111111111111" DEBUG=1 localstack start`
2. Deploy anything with an ARN (in this example I deployed a lambda)
3. Check the ARN. Example output for lambda:
```json
$ awslocal lambda list-functions
{
    "Functions": [
        {
            "FunctionName": "localtest-local-hello",
            "FunctionArn": "arn:aws:lambda:us-east-1:000000000000:function:localtest-local-hello",
            "Runtime": "nodejs10.x",
            "Role": "test_role",
            "Handler": "handler.hello",
            "CodeSize": 3077,
            "Description": "",
            "Timeout": 6,
            "MemorySize": 1024,
            "LastModified": "2019-11-06T06:43:53.451+0000",
            "CodeSha256": "V77gR13o90ET7+XquXBBc3Rxr1qDu1bE7S+A0Wbx5ys=",
            "Version": "$LATEST",
            "TracingConfig": {
                "Mode": "PassThrough"
            },
            "RevisionId": "3d4ed679-c1a9-4b7e-ad9e-f27e8543c5e9"
        }
    ]
}
```

ARN is still 000000000000
global SERVICE_PORTS
    SERVICE_PORTS = service_ports or parse_service_ports()
    globs = globals()
    
    for key, value in six.iteritems(DEFAULT_SERVICE_PORTS):
        key_upper = key.upper().replace('-', '_')
        
        port_var_name = 'PORT_%s' % key_upper
        port_number = SERVICE_PORTS.get(key, 0)
        globs[port_var_name] = port_number
        url = 'http%s://%s:%s' % ('s' if USE_SSL else '', LOCALSTACK_HOSTNAME, port_number)
        
        url_key = 'TEST_%s_URL' % key_upper
        globs[url_key] = url
        
        os.environ[url_key] = url
    
    os.environ['LOCALSTACK_HOSTNAME'] = LOCALSTACK_HOSTNAME
def service_port(service_key):
    return SERVICE_PORTS.get(service_key, 0)
populate_configs()
if os.environ.get('DEBUG', '').lower() in TRUE_VALUES:
    logging.getLogger('').setLevel(logging.DEBUG)
    logging.getLogger('localstack').setLevel(logging.DEBUG)
BUNDLE_API_PROCESSES = True
USE_PROFILER = os.environ.get('USE_PROFILER', '').lower() in TRUE_VALUES
INBOUND_GATEWAY_URL_PATTERN = ('%s/restapis/{api_id}/{stage_name}/%s{path}' %
                               (TEST_APIGATEWAY_URL, PATH_USER_REQUEST))