code: def test_get_by_type_nested_sections(self):
      nav_cfg = [
          {
              "Section 1": [
                  {
                      "Section 2": [
                          {"Page": "page.md"},
                      ]
                  },
              ]
          },
      ]
      cfg = load_config(nav=nav_cfg, site_url="http://example.com/")
      fs = [
          File(
              "page.md",
              cfg.docs_dir,
              cfg.site_dir,
              cfg.use_directory_urls,
          )
      ]
      files = Files(fs)
      site_navigation = get_navigation(files, cfg)
      self.assertEqual(len(_get_by_type(site_navigation, Section)), 2)
  
imports: import sys
  import unittest
  from mkdocs.structure.files import File, Files, set_exclusions
  from mkdocs.structure.nav import Section, _get_by_type, get_navigation
  from mkdocs.structure.pages import Page
  from mkdocs.tests.base import dedent, load_config
label_desc: Use image node_id 17 for calling the SiteNavigationTests obj's underlying member method code with example usage: obj.test_get_by_type_nested_sections() without return types