This is a wonderful exercise which explains the concept of infinite loops.

"A hacker practices on HackerRank until getting to a rating of O(1) read as (Oh-one)"

An infinite loop in Ruby is of the form

loop do
end

Use an infinite loop and call the method coder.practice within it and break if coder.oh_one? is true.

break if conditions in Ruby are of the form

if <condition>
    break
end

or a one-liner

break if <condition>