I found a test utility. It hangs like this from LAN:
turnutils_uclient -p 5439 -w long_thing -v -y my.example.com
0: (1158733): INFO: IPv4. Connected from: 192.168.1.59:50155
0: (1158733): INFO: IPv4. Connected to: 1.2.3.4:5439
0: (1158733): INFO: allocate sent
turnutils_uclient -p 5439 -w long_thing -v -y my.example.com
0: (1158733): INFO: IPv4. Connected from: 192.168.1.59:50155
0: (1158733): INFO: IPv4. Connected to: 1.2.3.4:5439
0: (1158733): INFO: allocate sent
"