How to know if federation works as expected?

So, I have set up my own instance. However, I'm not sure that federation works as expected.

I can subscribe to other communities and I can post to them. However, if I check my alt accounts (on lemmy.ml and lemmy.world), the comment is sometimes not showing.

One comment was there, and I upvoted it from my alt. I then checked on my own server and the upvote was not there.

Am I missing something? Or is federation just "slow"?