'Calling /json/subscriptions/exist on a stream whose name is invalid (as
defined by valid_stream_name in zerver/views.py) should return a JSON
error.'

def test_subscriptions_exist_invalid_name(self):

    invalid_stream_name = ''
    result = self.client_post('/json/subscriptions/exists', {'stream': invalid_stream_name})
    self.assert_json_error(result, "Invalid    stream    name    ''")
