code: def test_print_structure(self):
      tableset = TableSet(self.tables.values(), self.tables.keys())
  
      output = StringIO()
      tableset.print_structure(output=output)
      lines = output.getvalue().strip().split("\n")
  
      self.assertEqual(len(lines), 5)
  
imports: import json
  import shutil
  from collections import OrderedDict
  from io import StringIO
  from agate import Table, TableSet
  from agate.computations import Formula
  from agate.data_types import Number, Text
  from agate.testcase import AgateTestCase
label_desc: Use image node_id 19 for calling the TestTableSet obj's underlying member method code with example usage: obj.test_print_structure() without return types