What is the best way to test game networking code for stability and reliability?

Simulating network conditions allows developers to replicate various scenarios, like poor connections or high traffic, to anticipate how the game will perform in less-than-ideal environments. As Andy Hunt once said, "You can't wait for inspiration. You have to go after it with a club." Simulating network conditions is that proactive approach; it helps identify vulnerabilities, assesses how the game behaves under stress, and empowers developers to preemptively optimize the code for a smoother gaming experience. By replicating real-world challenges, this testing method ensures the game remains robust and enjoyable regardless of varying network circumstances.

Testing game networking code with real players helps to replicate real-world scenarios and interactions, and identify potential issues that automated or simulated tests might miss. As Will Wright, the creator of SimCity, once said, "A game is never finished, only abandoned." Real players bring diverse network conditions, behaviors, and hardware setups, revealing bugs, latency issues, and stability problems that can only be detected in live, dynamic environments. Their unpredictable actions stress-test the code, ensuring it performs reliably when deployed to a broader audience. Ultimately, real player testing is the litmus test for a game's network stability and reliability.

There's really nothing better than having real world data. Simulating network conditions is fine for ideal environments. However ideal environments often go out the window when the unpredictability of users is introduced into the system. Introducing users into the system allows the developer to create and test contingency plans to combat nefarious actors. As with almost any testing scenario, testers should be given incentive to break the system.

You can control everything ranging from syncing of actions to storage and retrieval of player data via code. Same goes for matchmaking. However, ping cannot be controlled. In many multiplayer SDKs, you can however, whitelist a certain set of areas and matchmaking is done based on that. Other than that, make sure you do not put stress on the server with irrelevant processing which can easily be handled on client. This can, in turn, give you some edge when players are facing high latency issues.