README.md

Extracting the bar calculation into a separate object, which doesn't know about Foo, allows us to test this code in more isolation and to easily change it in the future, because of its reduced context.

bar_calculation.rb

class BarCalculation
  def initialize(input1, input2)
    @input1 = input1
    @input2 = input2
  end
  
  def calculate
    # ..... the same bad code
  end
  
  private
  attr_reader :input1, :input2
end

better_foo.rb

class BetterFoo
  private
  
  def bar
    new BarCalculator(intpu1, input2).calculate
  end
end

foo.rb

class Foo
  private
  
  def bar
    # .... some really bad code @#$@#$
  end
end