Looks like a error in the some test cases : while n is negative - expected result is positive number for some test case
Ex:fib(-6) expected 8

C# solution the same thing, as below :
Compilation succeeded - 1 warning(s)
{"stdout":"","stderr":"/tmp/csharp11653-23-v5rpbw/fixture.cs(8,20): warning CS0414: The private field `KataSolution.random' is assigned but its value is never used\n","wallTime":0}

Can you explain me why the warning interrupts the compilation? I how i can fix this?