def test_var_to_placeholder(self):
     with self.subTest():
         self.assertEqual(EP.var_to_placeholder('+'), '+')
     with self.subTest():
         self.assertEqual(EP.var_to_placeholder('*'), '*')
     with self.subTest():
         self.assertEqual(EP.var_to_placeholder('~'), '~')
     with self.subTest():
         self.assertEqual(EP.var_to_placeholder('>'), '>')
     with self.subTest():
         self.assertEqual(EP.var_to_placeholder('='), '=')
     with self.subTest():
         self.assertEqual(EP.var_to_placeholder('('), '(')
     with self.subTest():
         self.assertEqual(EP.var_to_placeholder(')'), ')')
     with self.subTest():
         self.assertEqual(EP.var_to_placeholder('true'), 'true')
     with self.subTest():
         self.assertEqual(EP.var_to_placeholder('false'), 'false')
     with self.subTest():
         self.assertIsNone(EP.var_to_placeholder(None))
     with self.subTest():
         self.assertEqual(EP.var_to_placeholder('p'), 'VAR')
     with self.subTest():
         self.assertEqual(EP.var_to_placeholder('q'), 'VAR')
     with self.subTest():
         self.assertEqual(EP.var_to_placeholder('andorvar'), 'VAR')