Example of using an anonymous class to build an RSpec custom Matcher

gistfile1.rb

def be_guest_member_of(expected)
  Class.new do
    def initialize(expected)
      @expected = expected
    end

    def matches?(target)
      @target = target
      @target.memberships.where(role: "guest").map(&:network).include? @expected
    end

    def failure_message_for_should
      "expected #{@target.inspect} to be a guest member of #{@expected.inspect}"
    end

    def failure_message_for_should_not
      "expected #{@target.inspect} to not be a guest member of #{@expected.inspect}"
    end
  end.new(expected)
end

# usage example
user1.should be_guest_member_of network2
user1.should_not be_guest_member_of network1

@obie every time you use the matcher, a new class is created and after that is instantiated.

You may want to do that:

module Matchers
  extend RSpec::Matchers::DSL

  matcher :have_disabled_field do |field|
    match do |page|
      page.find_field(field)[:disabled].should eq 'true'
    end

    failure_message_for_should do |page|
      "expected #{page.text.inspect} to have disabled field #{field.inspect}"
    end

    failure_message_for_should_not do |page|
      "expected #{page.text.inspect} not to have disabled field #{field.inspect}"
    end
  end

  matcher :have_disabled_button do |field|
    match do |page|
      page.find_button(field)[:disabled].should eq 'true'
    end

    failure_message_for_should do |page|
      "expected #{page.text.inspect} to have disabled button #{field.inspect}"
    end

    failure_message_for_should_not do |page|
      "expected #{page.text.inspect} not to have disabled button #{field.inspect}"
    end
  end

  matcher :have_notice do |notice|
    match do |page|
      page.should have_css(".notice", :text => notice)
    end

    failure_message_for_should do |page|
      "expected #{page.text.inspect} to have notice #{notice.inspect}"
    end

    failure_message_for_should_not do |page|
      "expected #{page.text.inspect} not to have notice #{notice.inspect}"
    end
  end

  matcher :have_alert do |alert|
    match do |page|
      page.should have_css(".alert", :text => alert)
    end

    failure_message_for_should do |page|
      "expected #{page.text.inspect} to have alert #{alert.inspect}"
    end

    failure_message_for_should_not do |page|
      "expected #{page.text.inspect} not to have alert #{alert.inspect}"
    end
  end
end

RSpec.configure do |config|
  config.include Matchers, :type => :request
end

I didn't make a benchmark but is obviously that creating a new class every time you use the matcher will be slow :)

@supaspoida, methinks the more appropriate question here would be as to what is the specific benefit of that class being anonymous?

@dexterous No benefit, in fact probably harmful given the matcher DSL example provided by @sobrinho :)

@obie yeah; in fact, given that the class isn't built dynamically using the parameter to be_guest_member_of, simply pulling the class out of the function and naming it might boost, not just performance, but also clarity of intent by at least an order of magnitude.

RSpec::Matchers also has a .define that will take care of the config stuff for you. Throw it in spec/support like so:

RSpec::Matchers.define :be_guest_member_of do |expected|
  match do |target|
    target.memberships.where(role: "guest").map(&:network).include? expected
  end

  failure_message_for_should do |target|
    "expected #{target.inspect} to be a guest member of #{expected.inspect}"
  end

  failure_message_for_should_not do |target|
    "expected #{target.inspect} to not be a guest member of #{expected.inspect}"
  end
end

I would argue that this is the cleanest way to go, but make no claims regarding performance.

I do think in this case that reaching through so many associations like that is an indicator that the design should change to improve the tests though.