Technically there is no difference. The compiler will change this version to a "return" statement.
So it is just syntactic sugar and personal preference.
I personally like to use the lambda style if my method does not have much logic like in this case. This reduces your code to the important statement without the noise of the brackets, etc.

That is the first value to start with for the aggregation because Aggregate will otherwise throw an InvalidOperationException if the array is empty. Just extend your tests with an empty array to see the difference :)

I adjusted that. Also the solution was in the preloaded code with the same namespace as the tests.
So the tests were always using the preloaded solution instead of the user solution which has no namespace.

Forgot to mark issue as resolved

Thank you very much! I corrected it :)

Did not know that

Thank you. Approved :)

Good translation Mr. Kartoffelsalat. Time to press the green button ;)

Just had a look.
But there seems to be a problem in the random tests.
If I run the initial solution which just returns an empty string, the random tests succeed already.
Also please check for an upper digit before adding an underscore in the random generator.
If that it working I will publish it. Thanks for the translation :)