code: def test_auth_but_no_cred(keyring=None):
      authenticator = HTMLFormAuthenticator("")
      # Replying 'no' to the set credentials prompt should raise ValueError
      assert_raises(
          ValueError,
          HTTPDownloader,
          credential=None,
          authenticator=authenticator,
      )
      # Reply 'yes' and set test user:pass at the next set credentials prompt
      downloader = HTTPDownloader(
          credential=None, authenticator=authenticator
      )
      # Verify credentials correctly set to test user:pass
      assert_equal(downloader.credential.get("user"), "testlogin")
      assert_equal(
          downloader.credential.get("password"), "testpassword"
      )
  
imports: import builtins
  import os
  import re
  import time
  from calendar import timegm
  from os.path import join
  from datalad.downloaders.tests.utils import get_test_providers
  from datalad.support.network import download_url, get_url_straight_filename
  from datalad.utils import ensure_unicode
  from ...support.exceptions import AccessFailedError
  from ..base import BaseDownloader, DownloadError, IncompleteDownloadError, NoneAuthenticator
  from ..credentials import LORIS_Token, Token, UserPassword
  from ..http import HTMLFormAuthenticator, HTTPBaseAuthenticator, HTTPBearerTokenAuthenticator, HTTPDownloader, process_www_authenticate
  from unittest.mock import patch
  from ...support.exceptions import AccessDeniedError, AnonymousAccessDeniedError
  from ...support.network import get_url_disposition_filename
  from ...support.status import FileStatus
  from ...tests.utils_pytest import SkipTest, assert_equal, assert_false, assert_greater, assert_in, assert_not_in, assert_raises, known_failure_githubci_win, ok_file_has_content, serve_path_via_http, skip_if, skip_if_no_network, swallow_logs, swallow_outputs, use_cassette, with_fake_cookies_db, with_memory_keyring, with_tempfile, with_testsui, with_tree, without_http_proxy
  from ...utils import read_file
label_desc: Use image node_id 16 for calling a global function with example usage: test_auth_but_no_cred(keyring) without return types