code: def test_optionals(self) -> None:
      grammar = """
              start: expr NEWLINE
              expr: ['a'] ['b'] 'c'
          """
      self.assertEqual(
          self.calculate_first_sets(grammar),
          {
              "expr": {"'c'", "'a'", "'b'"},
              "start": {"'c'", "'a'", "'b'"},
          },
      )
  
imports: import unittest
  from test import test_tools
  from typing import Dict, Set
label_desc: Use image node_id 3 for calling the TestFirstSets obj's underlying member method code with example usage: obj.test_optionals() without return types