Ruby 3.0 should be enabled, read this to learn how to do it

Please organize the structure of test fixture as following (although it has been mentioned in the attached link, I'm repeated here again)

describe "<This message should describe the categories of test groups inside this block>" do
  it "<A short message describing this test group>" do
    expect(...).to eq(...) #Assertions
    #Or Test.assert_equals(user_response, reference_response)
  end
end

https://www.codewars.com/kata/reviews/5fc774e4aa9a11000169be7e/groups/5fc7805eaa9a11000169bf62 --> DUE TO NO RANDOM TESTS

I think there are enough of fibonacci katas out there...

You've got integer overflow. Tests are invalid for big integers