Example custom matcher to use for testing roman numeral conversions

roman_numeral_custom_matcher.rb

RSpec::Matchers.define :be_converted_to do |expected|
  match do |actual|
    @result = Calculator.convert(actual)
    @result == expected
  end

  failure_message_for_should do
    "Expected #{actual} to be converted to #{expected}, but got #{@result}"
  end

  failure_message_for_should_not do
    "Expected #{actual} to not be converted of #{expected}"
  end

  description do
    "#{actual} be converted to #{expected}"
  end
end