code: def test_positive_lookahead(self) -> None:
      grammar = """
          start: expr NEWLINE
          expr: &'a' opt
          opt: 'a' | 'b' | 'c'
          """
      self.assertEqual(
          self.calculate_first_sets(grammar),
          {
              "expr": {"'a'"},
              "start": {"'a'"},
              "opt": {"'b'", "'c'", "'a'"},
          },
      )
  
imports: import unittest
  from test import test_tools
  from typing import Dict, Set
label_desc: Use image node_id 14 for calling the TestFirstSets obj's underlying member method code with example usage: obj.test_positive_lookahead() without return types