Nice!

Thanks!! I was about to rage - saved me! :o)

I was code blind, after having mutation issues, thank you!!!!

Read the error message, it's not about mutation:

#<TypeError: no implicit conversion from nil to integer>
main.rb:12:in `delete_at'
main.rb:12:in `remove_smallest'
main.rb:21:in `block (2 levels) in <main>'
/runner/frameworks/ruby/cw-2.rb:180:in `wrap_error'
/runner/frameworks/ruby/cw-2.rb:72:in `it'
/runner/frameworks/ruby/cw-2.rb:206:in `it'
main.rb:17:in `block in <main>'
/runner/frameworks/ruby/cw-2.rb:55:in `block in describe'
/runner/frameworks/ruby/cw-2.rb:46:in `measure'
/runner/frameworks/ruby/cw-2.rb:51:in `describe'
/runner/frameworks/ruby/cw-2.rb:202:in `describe'
main.rb:16:in `<main>'

Refactor your code.