My solution is passing all of the test cases, but does not pass the falsifiable test. I'm certain that what I'm doing fits the given pattern, so I'm not quite sure what I'm missing.

Also, it is telling me

expected: 150
but got: 0
-3

Is that a (negative) 3 ? I tried using absolute value, which doesn't help.

There is no reason to keep the entire array around.

def fibonacci(n, arr=[0, 1])
return n if (0..1).include? n
return arr.reduce(&:+) if n == 2
fibonacci(n - 1, [arr[1], arr.reduce(&:+)])
end