Issue 24297: Add a unittest that Lib/symbol.py is in sync with Grammar

Lib/test/test_symbol.py

+import unittest
+from test import support
+import filecmp
+import os
+import sys
+import subprocess
+
+
+SYMBOL_FILE              = support.findfile('symbol.py')
+GRAMMAR_FILE             = os.path.join(os.path.dirname(__file__),
+                                        '..', '..', 'Include', 'graminit.h')
+TEST_PY_FILE             = 'symbol_test.py'
+
+
+class TestSymbolGeneration(unittest.TestCase):
+
+    def _copy_file_without_generated_symbols(self, source_file, dest_file):
+        with open(source_file, 'rb') as fp:
+            lines = fp.readlines()
+        nl = lines[0][len(lines[0].rstrip()):]
+        with open(dest_file, 'wb') as fp:
+            fp.writelines(lines[:lines.index(b"#--start constants--" + nl) + 1])
+            fp.writelines(lines[lines.index(b"#--end constants--" + nl):])
+
+    def _generate_symbols(self, grammar_file, target_symbol_py_file):
+        proc = subprocess.Popen([sys.executable,
+                                 SYMBOL_FILE,
+                                 grammar_file,
+                                 target_symbol_py_file], stderr=subprocess.PIPE)
+        stderr = proc.communicate()[1]
+        return proc.returncode, stderr
+
+    @unittest.skipIf(not os.path.exists(GRAMMAR_FILE),
+                     'test only works from source build directory')
+    def test_real_grammar_and_symbol_file(self):
+        self._copy_file_without_generated_symbols(SYMBOL_FILE, TEST_PY_FILE)
+        self.addCleanup(support.unlink, TEST_PY_FILE)
+        self.assertFalse(filecmp.cmp(SYMBOL_FILE, TEST_PY_FILE))
+        self.assertEqual((0, b''), self._generate_symbols(GRAMMAR_FILE,
+                                                          TEST_PY_FILE))
+        self.assertTrue(filecmp.cmp(SYMBOL_FILE, TEST_PY_FILE))
+
+
+if __name__ == "__main__":
+    unittest.main()