Question: what makes this a private tor network?

[furkanmustafa]

I am still trying to learn and understand the mechanics here.

I have went through the source, but I couldn't figure this out.

config/torrc file has this line;

TestingTorNetwork 1

But any tor node can have that line, what prevents any external node from joining a private tor network?

I was excepting something like a shared-secret, or pub-key auth, something that will block unknown nodes. Am I thinking in the wrong direction?

If you have any links to any explanation/documents, that would be great help.

Thanks!