That is in principle correct, but since OP is using a throwaway and a know anonymous domain service. As long as he burns bridges after himself (eg. not making it into a adressable business later), there is not individual to deliver a letter to.
Might work for a while, but a dangerous game to play...
It’s a bit more nuanced, you don’t need a Impressum for purely personal websites without financial background. Evaluating a business idea would probably count as financial motive though, even if it isn’t currently monetized.
The economics don't matter, everything that is regularly updated or offers a service needs an Impressum. The exception for "purely personal or familial" use clearly doesn't apply here because a service is being provided actively.
It mandates a Impressum for „ geschäftsmäßige, in der Regel gegen Entgelt angebotene Telemedien“. If it’s not geschäftsmäßig (Business-Like?), you don’t need an Impressum. If you do it for free without any intention to make money now or later, it’s not geschäftsmäßig.
If I have a blog that I update regularly but don’t have any ads from or take donations for, I don’t need an Impressum.
Impressumspflicht only applies for commercial interests. If you are a company informing or even selling something, if you are an influencer making money of yourself, or even if you just have ads on your Pokemon-fanpage, then it counts as commercial interest.
But I don't see any direct monetary value on this site at the moment. There is not even a reputation-gain, as there is no personal information. So Impressumspflicht would not apply.
Likely nothing will happen, but the way it looks, it is not obvious it is only for testing and you now posted it in the open and there seems a comercial intent. The law is quite clear there last time I checked, it needs an adress. (Even for uncomercial projects it seems advisable).
