my_rspec_custom_matcher.rb

module MyRspecCustomMatcher

  class CheckAttributes
    attr_accessor :object, :expected_val, :actual_val, :attribute
    def initialize(expected)  
      @expected = expected  
    end  
    
    def matches?(actual)  
      self.object = actual
      # actual is object
      @expected.all? do |key, val|
        self.actual_val = object.send(key)
        self.expected_val = val
        self.attribute = key

        actual_val == expected_val
      end
    end
    
    def failure_message_for_should  
      "object of class #{object.class} should have '#{expected_val}' as #{attribute}, but has '#{actual_val}'"
    end  
  end  

  def have_these_attributes(expected)  
    CheckAttributes.new(expected)
  end

end

output.txt

$ rake
-- create_table(:users)
   -> 0.0359s
-- create_table(:apples)
   -> 0.0006s
-- initialize_schema_migrations_table()
   -> 0.0010s
-- assume_migrated_upto_version(1, "db/migrate")
   -> 0.0003s

User
- should be useful as a test of spec custom matchers
- should be cleaner this way
- example as a failing spec (FAILED - 1)

1)
'User example as a failing spec' FAILED
object of class User should have '363' as age, but has '367'
./user_spec.rb:31:

Finished in 0.036559 seconds

3 examples, 1 failure

Rakefile

ask :default do
  system("spec --color -f specdoc user_spec.rb")
end

user.rb

require 'rubygems'
require 'active_record'

ActiveRecord::Base.establish_connection(:adapter => "sqlite3", :database => ":memory:")

ActiveRecord::Schema.define(:version => 1) do

  create_table :users do |t|
    t.string  :login
    t.string  :full_name
    t.date    :date_of_birth
  end

  create_table :apples do |t|
    t.references :user
    t.string :color
  end
end

class User < ActiveRecord::Base
  has_many :apples
  before_create :set_login

  def age
    now = Time.now.utc.to_date
    now.year - date_of_birth.year - ((now.month > date_of_birth.month || (now.month == date_of_birth.month && now.day >= date_of_birth.day)) ? 0 : 1)
  end

  private
  def set_login
    self.login = full_name.downcase.gsub(/ /, "_")
  end

end

user_spec.rb

require 'user'
require 'my_rspec_custom_matcher'

Spec::Runner.configure do |config|
  config.include(MyRspecCustomMatcher)
end

describe User do
  before do
    u = User.create(:login => @login, :full_name => "Isaac Newton", :date_of_birth => "1643-01-04")
  end
  
  it "should be useful as a test of spec custom matchers" do
    user = User.find_by_full_name("Isaac Newton")

    user.login.should == "isaac_newton"
    user.age.should == 367
  end

  it "should be cleaner this way" do
    user = User.find_by_full_name("Isaac Newton")

    user.should have_these_attributes ({
        :login => "isaac_newton",
        :age => 367 })
  end

  it "example as a failing spec" do
    user = User.find_by_full_name("Isaac Newton")

    user.should have_these_attributes({
        :login => "isaac_newton",
        :age => 363 })
  end
  
end