I know, I was suggesting to try out atheism for someone who believes in something else.

All this to say that such suggestions do not make sense, a belief or lack of is not something which someone can "try out". I can imagine that following some major life events, for someone who is inclined to such a change, "trying out" is an option.

Having had all kind of dramatic events in my life I never felt the need to invoque a superior being. YMMV.

That's false though. You don't have to start out committed to anything. You can simply pick up a religious book or attend a religious service and see if it speaks to you.

Are you a believer? Do you think it is enough to just say "I do not believe anymore for the next 2 weeks", really meaning it? If so, it means that the faith was not very strong.

Except for some specific cases, one usually grows with a religion or non-religion and this deeply forges one's perspective.

I'm an adult convert. So what I'm telling you is, I didn't have to start out believing; just curious. Obviously atheism is different because there is no particular doctrine or liturgy to involve yourself in, but you could certainly read atheist polemic.