code: def test_subset_fonts():
      """Confirm subset_fonts is working."""
      if not hasattr(fitz, "mupdf"):
          print("Not testing 'test_subset_fonts' in classic.")
          return
      text = "Just some arbitrary text."
      arch = fitz.Archive()
      css = fitz.css_for_pymupdf_font("ubuntu", archive=arch)
      css += "* {font-family: ubuntu;}"
      doc = fitz.open()
      page = doc.new_page()
      page.insert_htmlbox(page.rect, text, css=css, archive=arch)
      doc.subset_fonts(verbose=True)
      found = False
      for xref in range(1, doc.xref_length()):
          if doc.xref_is_font(xref):
              if "+Ubuntu#20Regular" in doc.xref_object(xref):
                  found = True
                  break
      assert found is True
  
imports: import io
  import os
  import fitz
  import pickle
label_desc: Use image node_id 46 for calling a global function with example usage: test_subset_fonts() without return types