This version of Unity is unsupported.
Removed

Network.TestConnectionNAT

Obsolete public static ConnectionTesterStatus TestConnectionNAT();
Obsolete public static ConnectionTesterStatus TestConnectionNAT(bool forceTest);

Description

Test the connection specifically for NAT punch-through connectivity.

This is like Network.TestConnection except that a NAT punchthrough test is forced, even through the machine does not have a NAT address (private IP address) but a public address. See Network.TestConnection example code.