(disclosure: speaking as an Unordinal employee)
As Joe censored said photon would be a good option regarding the scope of your multiplayer.
You may have seen this but in case I will link it here: What are the pros and cons of available network solutions/assets
There you can see the pros and cons of every networking option out there, the more the merrier and it might help decide you what kind of game you want to make.
As for testing I have a suggestion (and this is where the disclosure becomes relevant), it is the Unordinal platform: Product - Next Generation Multiplayer Servers It’s extremely easy to set up and the hosting is free while developing with no CCU limit.