I understand "singleton" as "only one exists" and "it exists in the global scope". That is, if I create one instance of something in my `int main()` that's not

I understand "singleton" as "only one exists" and "it exists in the global scope". That is, if I create one instance of something in my `int main()` that's not enough for it to be a singleton. That's important, because there's more than one way to enter your program. Notably, tests don't flow through your main entrypoint.