code: def test_sectioning(app, status, warning):
      def getsects(section):
          if not isinstance(section, nodes.section):
              return [getsects(n) for n in section.children]
          title = section.next_node(nodes.title).astext().strip()
          subsects = []
          children = section.children[:]
          while children:
              node = children.pop(0)
              if isinstance(node, nodes.section):
                  subsects.append(node)
                  continue
              children = list(node.children) + children
          return [title, [getsects(subsect) for subsect in subsects]]
  
      def testsects(prefix, sects, indent=0):
          title = sects[0]
          parent_num = title.split()[0]
          assert prefix == parent_num, (
              "Section out of place: %r" % title
          )
          for i, subsect in enumerate(sects[1]):
              num = subsect[0].split()[0]
              assert re.match("[0-9]+[.0-9]*[.]", num), (
                  "Unnumbered section: %r" % subsect[0]
              )
              testsects(prefix + str(i + 1) + ".", subsect, indent + 4)
  
      app.build(filenames=[app.srcdir / "only.rst"])
      doctree = app.env.get_doctree("only")
      app.env.apply_post_transforms(doctree, "only")
  
      parts = [
          getsects(n)
          for n in [
              _n
              for _n in doctree.children
              if isinstance(_n, nodes.section)
          ]
      ]
      for i, s in enumerate(parts):
          testsects(str(i + 1) + ".", s, 4)
      assert (
          len(parts) == 4
      ), "Expected 4 document level headings, got:\n%s" % "\n".join(
          p[0] for p in parts
      )
  
imports: import re
  import pytest
  from docutils import nodes
label_desc: Use image node_id 1 for calling a global function with example usage: test_sectioning(app, status, warning) and returns: list, unknown