test: Add test that mainnet requires standard txs

Author: MarcoFalke

test/functional/feature_config_args.py

@@ -29,6 +29,11 @@ def test_config_file_parser(self):
             conf.write("wallet=foo\n")
         self.nodes[0].assert_start_raises_init_error(expected_msg='Error: Config setting for -wallet only applied on regtest network when in [regtest] section.')
 
+        with open(inc_conf_file_path, 'w', encoding='utf-8') as conf:
+            conf.write('regtest=0\n') # mainnet
+            conf.write('acceptnonstdtxn=1\n')
+        self.nodes[0].assert_start_raises_init_error(expected_msg='Error: acceptnonstdtxn is not currently supported for main chain')
+
         with open(inc_conf_file_path, 'w', encoding='utf-8') as conf:
             conf.write('nono\n')
         self.nodes[0].assert_start_raises_init_error(expected_msg='Error reading configuration file: parse error on line 1: nono, if you intended to specify a negated option, use nono=1 instead')