RSpec cache matcher

cache_matcher.rb

RSpec::Matchers.define :have_key do |expected|
  def value
    @value
  end

  def cache_record
    @cache_record
  end

  def has_cache_key?
    cache_record != nil
  end

  def matches_value?
    return true unless value.present?
    cache_record == value
  end

  match do |actual|
    @cache_record = actual.read(expected) 
    has_cache_key? && matches_value?
  end

  chain :with_value do |value|
    @value = value
  end

  failure_message_for_should do |actual|
    case
    when !has_cache_key?
      "expected to have a cache with key: '#{expected}', but did not"
    when !matches_value?
      "expected cache value for: '#{expected}' to be #{value}, but was #{cache_record}"
    end
  end

  failure_message_for_should_not do |actual|
    case
    when has_cache_key?
      "expected not to have a cache with key: '#{expected}', but did"
    end
  end
end