code: def test_nav_from_nested_files(self):
      expected = dedent(
          """
              Page(title=[blank], url='/')
              Section(title='About')
                  Page(title=[blank], url='/about/license/')
                  Page(title=[blank], url='/about/release-notes/')
              Section(title='Api guide')
                  Page(title=[blank], url='/api-guide/debugging/')
                  Page(title=[blank], url='/api-guide/running/')
                  Page(title=[blank], url='/api-guide/testing/')
                  Section(title='Advanced')
                      Page(title=[blank], url='/api-guide/advanced/part-1/')
              """
      )
      cfg = load_config(site_url="http://example.com/")
      fs = [
          "index.md",
          "about/license.md",
          "about/release-notes.md",
          "api-guide/debugging.md",
          "api-guide/running.md",
          "api-guide/testing.md",
          "api-guide/advanced/part-1.md",
      ]
      files = Files(
          [
              File(
                  s, cfg.docs_dir, cfg.site_dir, cfg.use_directory_urls
              )
              for s in fs
          ]
      )
      site_navigation = get_navigation(files, cfg)
      self.assertEqual(str(site_navigation).strip(), expected)
      self.assertEqual(len(site_navigation.items), 3)
      self.assertEqual(len(site_navigation.pages), 7)
      self.assertEqual(
          repr(site_navigation.homepage), "Page(title=[blank], url='/')"
      )
  
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 13 for calling the SiteNavigationTests obj's underlying member method code with example usage: obj.test_nav_from_nested_files() without return types