code: def test_screenshot_selenium_headstart(
      self, mock_sleep, mock_webdriver, mock_webdriver_wait
  ):
      webdriver = WebDriverSelenium("firefox")
      user = security_manager.get_user_by_username(
          app.config["THUMBNAIL_SELENIUM_USER"]
      )
      url = get_url_path(
          "Superset.slice", slice_id=1, standalone="true"
      )
      app.config["SCREENSHOT_SELENIUM_HEADSTART"] = 5
      webdriver.get_screenshot(url, "chart-container", user=user)
      assert mock_sleep.call_args_list[0] == call(5)
  
imports: import json
  import urllib.request
  from io import BytesIO
  from unittest import skipUnless
  from unittest.mock import ANY, call, MagicMock, patch
  import pytest
  from flask_testing import LiveServerTestCase
  from sqlalchemy.sql import func
  from superset import db, is_feature_enabled, security_manager
  from superset.extensions import machine_auth_provider_factory
  from superset.models.dashboard import Dashboard
  from superset.models.slice import Slice
  from superset.tasks.types import ExecutorType
  from superset.utils.screenshots import ChartScreenshot, DashboardScreenshot
  from superset.utils.urls import get_url_path
  from superset.utils.webdriver import WebDriverSelenium
  from tests.integration_tests.conftest import with_feature_flags
  from tests.integration_tests.fixtures.birth_names_dashboard import load_birth_names_dashboard_with_slices, load_birth_names_data
  from tests.integration_tests.test_app import app
  from .base_tests import SupersetTestCase
label_desc: Use image node_id 1 for calling the TestWebDriverSelenium obj's underlying member method code with example usage: obj.test_screenshot_selenium_headstart(mock_sleep, mock_webdriver, mock_webdriver_wait) without return types