Calc converter

converter_spec.rb

class Converter
  def initialize(input)
    @input = input
  end

  def convert
    "3 + 2"
  end
end

describe Converter do
  it "moves arguments around" do
    converter = Converter.new("(+ 3 2")
    converter.convert.should eq "3 + 2"
  end
end

This is obviously dumb because line 7 is just spitting back what line 14 is expecting, but your question was about structuring the spec file, so that's what I focused on. The next step here would be to add an assertion for your next test case and then actually begin the implementation.

Hope this helps!! :)